Make AccessibleObject trimmable

[JeremyKuhne]

In order for AOT/Trimming to be a viable option we need to change AccessibleObject to fully utilize native VARIANTs and pointers and use ComWrappers for our CCW projections.

There are a number of steps to this, including:

• Implement the CsWin32 IAccessible.Interface on AccessibleObject and have the existing public IAccessible interface projection just wrap this.
• Convert the UIA interfaces to use CsWin32.
• Ensure that we're using IManagedWrapper on all of our accessible objects.

AccessibleObject is a little difficult to make efficient due to it being public with numerous virtual members.

[elachlan]

Related: #9784