Add ScanOptions.NativeWindowHandle to scope Scans to rooted UIA sub-tree

[blackcatsonly]

Details

Adds:

• ScanOptions property settable to IntPtr for HWND of root of subtree to be scanned
• Teach PID descendants search to operate on HWND's subtree instead of GetRootElement
• Add Integration test for test app leaf node scan

Motivation

Proposal to address issue #1021

Context

I exposed internals of A11yAutomation to the Integration Tests project so I could find a relevant IUIAutomationElement for testing the ScanOptions' HWND constraint

You could implement this as a "ForWindowHandle()" constraint on the Config, but my external tools use the same scanner repeatedly - it's the individual Scans whose scope needs to be constrained.

Pull request checklist

• [X] Addresses an existing issue: #1021

[blackcatsonly]

@JGibson2019 Proposed change to allow ScanOptions to limit the scope of the Scan

[codeofdusk]

Please update the documentation (docs/AutomationReference.md and, for the CLI, the README.md under src/cli) with your new options.

[blackcatsonly]

@DaveTryon @codeofdusk Thanks for reviewing. I believe I've addressed all the comments from the first iteration. Would you please take a second look?

[codeofdusk]

@blackcatsonly Please update the AutomationReference docs.

[blackcatsonly]

@codeofdusk Thanks, missed than one! Updated in latest iteration.

[codeofdusk]

/azp run

[azure-pipelines[bot]]

Azure Pipelines successfully started running 1 pipeline(s).

[codeofdusk]

/azp run

[azure-pipelines[bot]]

Azure Pipelines successfully started running 1 pipeline(s).

[codeofdusk]

/azp run

[azure-pipelines[bot]]

Azure Pipelines successfully started running 1 pipeline(s).

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 94.23077% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 72.21%. Comparing base (4fc19c3) to head (aefe4da). Report is 383 commits behind head on main.

:exclamation: Current head aefe4da differs from pull request most recent head 37b41b3. Consider uploading reports for the commit 37b41b3 to get more accurate results

Files	Patch %	Lines
src/CLI/ScanRunner.cs	0.00%	1 Missing :warning:
src/Core/Bases/A11yElement.cs	0.00%	0 Missing and 1 partial :warning:
src/Desktop/UIAutomation/A11yAutomation.cs	96.55%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1022 +/- ## ========================================== - Coverage 73.70% 72.21% -1.49% ========================================== Files 398 424 +26 Lines 12046 13158 +1112 Branches 0 1413 +1413 ========================================== + Hits 8878 9502 +624 - Misses 3168 3243 +75 - Partials 0 413 +413 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[codeofdusk]

/azp run

[azure-pipelines[bot]]

Azure Pipelines successfully started running 1 pipeline(s).

[blackcatsonly]

Thanks @codeofdusk!