Utils::matchCaseReplacement searches for common prefix and suffix
between old and new file name und leaves them unchanged. This leads
to unexpected new file names.

E.g. when renaming MainWindow to MyMainWindow, this function computes
the prefix "m", the suffix "ainwindow.h" and only considers "yM" as
the middle part that is actually renamed.

Use a better algorithm to determine the new base name, and for
unclear cases fall back to the "Lower case file names" option
from Tools -> Options -> C++ -> File Naming.

Task-number: QTCREATORBUG-18592
Change-Id: I818f7d372102eb6e266123b2b4b6355f6fa28d64
Reviewed-by: Eike Ziller <eike.ziller@qt.io>