Restore old IA2 install/uninstall approach (#15525)
Replaces #15517
Summary of the issue:
It was pointed out by @michaelDCurran in #15517 (comment) that proxy registration in NVDA's main thread is essential.
Description of user facing changes
Probably nothing noticeable.
Description of development approach
Rename installIA2Support and uninstallIA2Support to installIA2SupportForThread and uninstallIA2SupportForTrhead, respectively. Introduce new installIA2Support and uninstallIA2Support wrappers that install/uninstall for the current thread. Also restored installation/uninstallation in NVDAHelper.py
