vcl: fix crashes when retrieving objects for MSAA

The ImplHandleGetObject() function modifies the Application Settings and
must take the SolarMutex for this; otherwise we get crashes when another
thread calls StyleSettings::GetPersonaHeader() during some unoapi test.

Also fix another HWND to long cast; use LRESULT which is Win32 for intptr_t.

Change-Id: I5580f88ed0a8e9955697655ace94584e2307982d
winaccessibility: fix my stupid mistake in createAggInstance

Change-Id: I7701021befcf1dbad85557c2095fe4bf0b4e0ff1
Revert "winaccessibility: let CoCreateInstance calls find the components"

This only works partially: the ClassObjects are only registered on the
main thread; CoCreateInstance on other threads still fails.

This reverts commit 29c6216af8c502f220bb84857d3dda901ddfd234.
winaccessibility: remove global g_acc_manager

It is possible to retrieve it via the AccTopWindowListener.

Change-Id: I6cc5ab25bc937d0d9f4de54a1bed09a76ce27491
vcl: check if AT is running before loading the library

... which should result in faster startup if it's disabled.

Change-Id: I39774b0a56f186d08270c2f17b2b20a823f21dc2