### Link to issue number:

Fixes nvaccess#13052

 ### Summary of the issue:

NVDA did not announce the first line indent for paragraphs
in LibreOffice Writer.

 ### Description of user facing changes

NVDA supports the "text-indent" IAccessible2 object attribute. As a
consequence, announcement of first line indent is now supported for
LibreOffice 25.8 and later.

 ### Description of development approach

Implement support for the "text-indent" object attribute as
specified in the
[IAccessible2 object attribute specification](https://github.com/LinuxA11y/IAccessible2/blob/master/spec/objectattributes.md),
which references the [CSS spec](https://www.w3.org/TR/CSS2/text.html#propdef-text-indent)
that explains:

> This property specifies the indentation of the first line
> of text in a block container.

https://gerrit.libreoffice.org/c/core/+/180574 implements
support in LibreOffice, i.e. reporting of that attribute by
LibreOffice.

This commit implements evaluation of that IAccessible2
object attribute by NVDA.

As recommended in the IAccessible2 object attribute spec,
LibreOffice reports the indentation in mm. Add a helper
method that converts that to either cm or inches, depending
on whether use of imperial measurements is enabled.

 ### Testing strategy:

1. start NVDA
2. open sample document https://bugs.documentfoundation.org/attachment.cgi?id=198672
   in LibreOffice Writer (current development version also
   including above-mentioned LibreOffice change)
3. move focus to the second paragraph that has a first line
   indentation of 1 cm set
4. request announcement of text formatting by pressing NVDA+F
5. Make sure that what NVDA says includes the first line indent
    ("first line indent 1.00 centimetre")

 ### Known issues with pull request:

None

 ### Code Review Checklist:

- [x] Documentation:
  - Change log entry
  - User Documentation
  - Developer / Technical Documentation
  - Context sensitive help for GUI changes
- [x] Testing:
  - Unit tests
  - System (end to end) tests
  - Manual testing
- [x] UX of all users considered:
  - Speech
  - Braille
  - Low Vision
  - Different web browsers
  - Localization in other languages / culture than English
- [x] API is compatible with existing add-ons.
- [x] Security precautions taken.

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