HLSPlaylistStructure Key Index Tags Refactor (Redo)

[gvb26]

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Addresses an issue where for some partners' (Cox) content is causing a crash when DAI is enabled. Was traced back to how we are handling tags.

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Change Notes

• Refactors Key index tag logic within HLSPlaylistStructureConstructor
• Added few edge case unit tests to HLSPlaylistStructureTests

Pre-submission Checklist

• I ran the unit tests locally before checking in.
• I made sure there were no compiler warnings before checking in.
• I have written useful documentation for all public code.
• I have written unit tests for this new feature.

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