replace ExtensionSystem::PluginManager::instance()->getObject<Core::ICore>() by Core::ICore::instance()

forward declaration is sufficient.

Details:  - Naming convention

Details:  - Conform to naming convention

Details:  - To make it conform to naming convention.

Fixes: Random enabling of submit/diff buttons when switching contexts (viewing diffs) from the submit editor

Details: Register actions directly

Task: 205821
RevBy: con
Details:  Add a IVersionControl to git. Extend IF to able to return a name and add enabling options. Connect project explorer to enable the right VCS.