[Backport to release/10.0]: Clipboard.GetText(TextDataFormat.Rtf) does not retrieve RTF that lacks a null terminating character

[SimonZhao888]

Backport #14461 to release/10.0

Fixes #14458

In ReadStringFromHGLOBAL method requires a null terminator to determine string length. The format dispatch switch groups RTF (a registered format) with CF_TEXT and CF_OEMTEXT (standard formats), routing RTF through this null-termination-required path.Composition.NativeToManagedAdapterReadStringFromHGLOBAL()

When external applications (PowerPoint, etc.) place RTF on the clipboard without a null terminator — which is valid per the Windows clipboard spec — the method returns instead of the actual RTF content.string.Empty

Proposed changes

• Add a new method ReadRegisteredFormatStringFromHGLOBAL(HGLOBAL, Encoding) to handle the CF_RTF format without a null terminator.

Customer Impact

• Clipboard.GetText(TextDataFormat.Rtf) can retrieve RTF that lacks a null terminating character.

Regression?

• Yes- regression PR Handle unterminated string data in DataObject #13949.

Risk

• Minimal

Test methodology

• Manual testing
• Unit test

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

❌ Patch coverage is 69.56522% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.10915%. Comparing base (e02e4db) to head (af1f6dd).
⚠️ Report is 6 commits behind head on release/10.0.

Additional details and impacted files

@@                  Coverage Diff                   @@
##           release/10.0      #14527         +/-   ##
======================================================
+ Coverage      77.10887%   77.10915%   +0.00028%     
======================================================
  Files              3273        3273                 
  Lines            645062      645083         +21     
  Branches          47704       47708          +4     
======================================================
+ Hits             497400      497418         +18     
- Misses           143986      143989          +3     
  Partials           3676        3676                 

Flag	Coverage Δ
Debug	77.10915% <69.56522%> (+0.00028%)	⬆️
integration	18.98920% <0.00000%> (+0.00035%)	⬆️
production	51.93139% <69.56522%> (+0.00245%)	⬆️
test	97.40991% <ø> (ø)
unit	49.34416% <69.56522%> (-0.00013%)	⬇️

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[LeafShi1]

@SimonZhao888 For backport PRs, screenshots are not required, however, the "Test methodology," "Regression," and associated issues sections must be filled out in detail. Please refer to the PR #14121.

[KlausLoeffelmann]

Looks good to me - approved.
One thing, though:

We should add (as a follow-up PR, not in the context of this one) one additional test, where we test RTF with a terminator to establish, that the existing behavior really remains.