Add support for YANG file extension and analyzer support (#4415)

[soninishank]

Summary

This pull request adds support for the YANG file extension in OpenGrok:

• Recognizes .yang files for indexing
• Integrates analyzer support
• Adds YANG to the UI file type selector
• Includes basic indexing tests

Fixes: #4415

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Signed-off-by: Nishank Soni soninishank8@gmail.com

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[soninishank]

I signed the OCA in a personal capacity and received a confirmation also after signing all docs on docusign.

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