Windows Accessibility Bridge.

This code provides a bridge between our internal Accessibility
interfaces (implemented on all visible 'things' in the suite: eg.
windows, buttons, entry boxes etc.) - and the Windows MSAA /
IAccessible2 COM interfaces that are familiar to windows users and
Accessible Technologies (ATs) such as the NVDA screen reader.

The code breaks into three bits:

source/service/
	+ the UNO service providing the accessibility bridge.
	  It essentially listens to events from the LibreOffice
	  core and creates and synchronises COM peers for our
	  internal accessibilty objects when events arrive.

source/UAccCom/
	+ COM implementations of the MSAA / IAccessible2 interfaces
	  to provide native peers for the accessbility code.

source/UAccCOMIDL/
	+ COM Interface Definition Language (IDL) for UAccCom.

Here is one way of visualising the code / control flow

VCL <-> UNO toolkit <-> UNO a11y <-> win a11y <-> COM / IAccessible2
vcl/ <-> toolkit/ <-> accessibility/ <-> winaccessibility/ <-> UAccCom/


Debugging / playing with winaccessibility

You need to enable 'experiemental mode' in Tools->Options. After
that NVDA should work as expected. In order to use 'accprobe' to debug
it is necessary to override the check for whether an AT (like NVDA) is
running; to do that use:

SAL_FORCE_IACCESSIBLE2=1 soffice.exe -writer

Then you can use accprobe to introspect the accessibility hierarchy
remotely, checkout:

http://accessibility.linuxfoundation.org/a11yweb/util/accprobe/