Add narrator announcement for tooltip information icon

[sshubhavee]

Description

Accessibility: Source info and Sample info icon buttons in the shared page header now expose accurate, contextual narration text and tooltip information for the active control instead of generic text.

Motivation and Context

Narrator was not consistently announcing meaningful supplemental info for the Source popup info icon (Info, button without useful context).

Bug Item: https://microsoft.visualstudio.com/OS/_workitems/edit/59759269

How Has This Been Tested?

The change was tested via 2 methods:

1. Build validation: Successful build in developer environment.
2. Manual Functional Verification: Local deployment of branch in dev environment via Visual Studio which deploys the WinUI Gallery Dev app locally.

Screenshots (if appropriate):

Before:

After:

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

[ayushjai19]

@sshubhavee have you validated that after this change the narrator is properly announcing the tooltip? Can you please attach a video with the fix.
I see you have changed the text string of sample page icon as well, please include that as well in the test video.

[ayushjai19]

/azp run

[niels9001]

@ayushjai19 @sshubhavee Wasn't the bug already resolved in: #2110?

[sshubhavee]

@ayushjai19 @sshubhavee Wasn't the bug already resolved in: #2110?

@niels9001, I checked the WinUI Gallery and I don't see the "control type" in the tooltip info text, neither is the "control type" announced by narrator

If you check out the attached screenshots, this PR also ensures that control type is announced by narrator and is present in tooltip.
Please let me know if I am missing some context.

[niels9001]

@ayushjai19 @sshubhavee Wasn't the bug already resolved in: #2110?

@niels9001, I checked the WinUI Gallery and I don't see the "control type" in the tooltip info text, neither is the "control type" announced by narrator

If you check out the attached screenshots, this PR also ensures that control type is announced by narrator and is present in tooltip. Please let me know if I am missing some context.

I think the earlier fix was barebones but met a11y requirements.. Your fix is definitely better :)!

[niels9001]

/azp run