Move some docs from .qdoc into .cpp

As we may not have the doc landing page once integrating into
some other Qt module.

src/rhi/doc/src/qtrhi-index.qdoc

@@ -38,61 +38,12 @@ graphics APIs, such as, \l{https://www.khronos.org/opengl/}{OpenGL},
 \l{https://developer.apple.com/metal/}{Metal}, and
 \l{https://www.khronos.org/vulkan/}{Vulkan}.
 
-Some of the main design goals are:
-
-\list
-
-\li Simple, minimal, understandable, extensible. Follow the proven path of the
-Qt Quick scenegraph.
-
-\li Aim to be a product - and in the bigger picture, part of a product (Qt) -
-that is usable out of the box both by internal (such as, Qt Quick) and,
-eventually, external users.
-
-\li Not a complete 1:1 wrapper for any of the underlying APIs. The feature set
-is tuned towards the needs of Qt's 2D and 3D offering (QPainter, Qt Quick, Qt
-3D Studio). Iterate and evolve in a sustainable manner.
-
-\li Intrinsically cross-platform, without reinventing: abstracting
-cross-platform aspects of certain APIs (such as, OpenGL context creation and
-windowing system interfaces, Vulkan instance and surface management) is not in
-scope here. These are delegated to the existing QtGui facilities (QWindow,
-QOpenGLContext, QVulkanInstance) and its backing QPA architecture.
-
-\endlist
-
 The main class in the module is QRhi. Each QRhi instance is backed by a backend
 for a specific graphics API. The selection of the backend is a run time choice
 and is up to the application or library that creates the QRhi instance. Some
 backends are available on multiple platforms (OpenGL, Vulkan, Null), while APIs
-specific to a given platform are only available when running on the platform in
-question.
-
-The available backends currently are:
-
-\list
-
-\li OpenGL 2.1 or OpenGL ES 2.0 or newer. Some extensions are utilized when
-present, for example to enable multisample framebuffers.
-
-\li Direct3D 11.1
-
-\li Metal
-
-\li Vulkan 1.0, optionally with some extensions that are part of Vulkan 1.1
-
-\li Null - A "dummy" backend that issues no graphics calls at all.
-
-\endlist
-
-In order to allow shader code to be written once in Qt applications and
-libraries, all shaders are expected to be written in a single language which is
-then compiled into SPIR-V. Versions for various shading language are then
-generated from that, together with reflection information (inputs, outputs,
-shader resources). This is then packed into easily and efficiently serializable
-QRhiShader instances. The compilers and tools to generate such shaders are not
-part of the Rhi module, but the core classes for using such shaders,
-QRhiShader and QRhiShaderDescription, are.
+specific to a given platform (Direct3D, Metal) are only available when running
+on the platform in question.
 
 \section1 Table of Contents
 

src/rhi/qrhi.cpp

@@ -59,12 +59,35 @@ QT_BEGIN_NAMESPACE
 
     \brief Accelerated 2D/3D graphics API abstraction.
 
-     QRhi is an abstraction for hardware accelerated graphics APIs, such as,
-     \l{https://www.khronos.org/opengl/}{OpenGL},
-     \l{https://www.khronos.org/opengles/}{OpenGL ES},
-     \l{https://docs.microsoft.com/en-us/windows/desktop/direct3d}{Direct3D},
-     \l{https://developer.apple.com/metal/}{Metal}, and
-     \l{https://www.khronos.org/vulkan/}{Vulkan}.
+    The Qt Rendering Hardware Interface is an abstraction for hardware accelerated
+    graphics APIs, such as, \l{https://www.khronos.org/opengl/}{OpenGL},
+    \l{https://www.khronos.org/opengles/}{OpenGL ES},
+    \l{https://docs.microsoft.com/en-us/windows/desktop/direct3d}{Direct3D},
+    \l{https://developer.apple.com/metal/}{Metal}, and
+    \l{https://www.khronos.org/vulkan/}{Vulkan}.
+
+    Some of the main design goals are:
+
+    \list
+
+    \li Simple, minimal, understandable, extensible. Follow the proven path of the
+    Qt Quick scenegraph.
+
+    \li Aim to be a product - and in the bigger picture, part of a product (Qt) -
+    that is usable out of the box both by internal (such as, Qt Quick) and,
+    eventually, external users.
+
+    \li Not a complete 1:1 wrapper for any of the underlying APIs. The feature set
+    is tuned towards the needs of Qt's 2D and 3D offering (QPainter, Qt Quick, Qt
+    3D Studio). Iterate and evolve in a sustainable manner.
+
+    \li Intrinsically cross-platform, without reinventing: abstracting
+    cross-platform aspects of certain APIs (such as, OpenGL context creation and
+    windowing system interfaces, Vulkan instance and surface management) is not in
+    scope here. These are delegated to the existing QtGui facilities (QWindow,
+    QOpenGLContext, QVulkanInstance) and its backing QPA architecture.
+
+    \endlist
 
     Each QRhi instance is backed by a backend for a specific graphics API. The
     selection of the backend is a run time choice and is up to the application
@@ -73,6 +96,32 @@ QT_BEGIN_NAMESPACE
     platform are only available when running on the platform in question (Metal
     on macOS/iOS/tvOS, Direct3D on Windows).
 
+    The available backends currently are:
+
+    \list
+
+    \li OpenGL 2.1 or OpenGL ES 2.0 or newer. Some extensions are utilized when
+    present, for example to enable multisample framebuffers.
+
+    \li Direct3D 11.1
+
+    \li Metal
+
+    \li Vulkan 1.0, optionally with some extensions that are part of Vulkan 1.1
+
+    \li Null - A "dummy" backend that issues no graphics calls at all.
+
+    \endlist
+
+    In order to allow shader code to be written once in Qt applications and
+    libraries, all shaders are expected to be written in a single language
+    which is then compiled into SPIR-V. Versions for various shading language
+    are then generated from that, together with reflection information (inputs,
+    outputs, shader resources). This is then packed into easily and efficiently
+    serializable QRhiShader instances. The compilers and tools to generate such
+    shaders are not part of QRhi, but the core classes for using such shaders,
+    QRhiShader and QRhiShaderDescription, are.
+
     \section2 Design Fundamentals
 
     A QRhi cannot be instantiated directly. Instead, use the create()