Mark globalVars for deprecation (#14050)
Supersedes #14037
See also #14049
Summary of the issue:
#14037 was closed because there was no way to preserve backwards compatibility.
This is the case for any module level variable which the NVDA API expects to support assignment (see also #14049).
globalVars contains many NVDA state variables which should not be changed by add-on authors.
As a result, globalVars should eventually be deprecated, in favour of encapsulation of these variables.
This will make retaining backwards compatibility possible in the future.
Description of user facing changes
None
Description of development approach
Added a deprecation warning and strategy to the docstring of globalVars.
Encapsulated some less used globalVars to provide an example of what the future API should look like.
runningAsSource was moved from globalVars as this is an unreleased variable. (#14015)
_allowDeprecatedAPI was moved as it is internal code.
