IA2: Evaluate "level" object attribute (#15882)
Fixes #15881
Summary of the issue:
The "level" object attribute for IAccessible2 to specify the level of a heading is both mentioned in the Core Accessibility API Mappings specification and in the IAccessible2::groupPosition documentation. However, NVDA was not supporting/evaluating this object attribute in order to determine the heading level, resulting in the heading level no longer getting announced once LibreOffice only reports the "level" attribute as specified and no longer the custom "heading-level" attribute that NVDA's soffice app module relies on.
Description of user facing changes
Reporting heading levels also works for LibreOffice version 24.2 and greater.
Description of development approach
Add handling for the "level" IAccessible2 object attribute when determining position info for an IAccessible2 object. In the soffice app module, add a comment that the custom "heading-level" attribute is only needed for Apache OpenOffice by now, since LibreOffice has already been reporting the "level" object attribute in addition to the "heading-level" attribute since LibreOffice 5.0.
