Fix duplicate stringTable elements in instrumentation manifest

[Copilot]

• [x] Investigate and understand the root cause of duplicate stringTable elements in GetManifestForRegisteredProvider()
• [x] Implement fix using HashSet to track emitted string IDs
• [x] Replace string.Format calls with string interpolation
• [x] Add unit test to verify no duplicate string IDs in stringTable
• [x] Build the changes
• [x] Run code review
• [x] Run security analysis with CodeQL

Original prompt

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This section details on the original issue you should resolve

<issue_title>instrumentation manifest - duplicate stringTable elements</issue_title> <issue_description>The stringTable in the instrumentation manifest generated by GetManifestForRegisteredProvider() can have duplicate elements.

e.g. Microsoft-JScript provider's manifest includes -

<string id="map_MethodAddressRangeMapJITLoopBody" value="JITLoopBody" />        
<string id="map_MethodAddressRangeMapJITLoopBody" value="JITLoopBody" />        
<string id="map_MethodAddressRangeMapJITLoopBody" value="JITLoopBody" />        
<string id="map_MethodAddressRangeMapJITLoopBody" value="JITLoopBody" />        
<string id="map_MethodAddressRangeMapJITLoopBody" value="JITLoopBody" />        
<string id="map_MethodAddressRangeMapJITLoopBody" value="JITLoopBody" />        
<string id="map_MethodAddressRangeMapJITLoopBody" value="JITLoopBody" />        
<string id="map_MethodAddressRangeMapJITLoopBody" value="JITLoopBody" />
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes microsoft/perfview#1069

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[Copilot]

@copilot, please address these comments.

Also, please add a new unit test that validates that the fix works. Use a provider that is known to exist on all machines, such as "Microsoft-Windows-DotNETR...

Addressed the string interpolation comment and added a new unit test GetManifestForRegisteredProvider_NoDuplicateStringTableEntries that validates no duplicate string IDs exist in the generated manifest. The test uses Microsoft-Windows-DotNETRuntime provider and is marked as Windows-only using [WindowsFact] since GetManifestForRegisteredProvider requires Windows TDH APIs. See commit a0fb478.