CppTools: Tests: Fix crash in test_modelmanager_gc_if_last_cppeditor_closed

The project that was referenced at cppeditor.cpp:711 was already
deleted. CppModelManager::m_fileToProjectParts contained outdated
information. Now it is updated if a project is closed.

Exposed by commit d411c07.

Change-Id: I6fee93a02c72a045dd44a05723ab39a1eeec616e
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>
TextEditor: Clarify "Using keyboard shortcut (Alt)" in the settings.

In Tools > Options > Text Editor > Behavior > "Mouse and Keyboard"
the position of the checkbox "Using keyboard shortcut (Alt)" had an
unclear relation to the mouse settings above. Users assumed those two
were linked.

Now the checkbox is moved above the mouse settings and it is not
indentend any more. Further, both settings labels were slightly changed
to clarify that.

Task-number: QTCREATORBUG-10178
Change-Id: I01c01850213f1f34ed34ebd0d87e25243229b2d4
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>
TextEditor: Fix displaying function proposals

In commit 3a64f8a the condition for displaying a replacement proposal
was strengthened by making it only depend on the current proposal
m_proposal. Since FuntionHintProposals were fragile, the automatic
proposal timer was restarted in notifyChange() and as consequence the
proposal was reset.

Fixed by declaring that FunctionHintProposal are not fragile.

Task-number: QTCREATORBUG-10283
Change-Id: I60828d733b781279be51228bd10d49f828aebe2b
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>