Prefer public IDs when comparing grammar descriptors

[raducoravu]

Fix for #3568 Prefer public IDs when comparing descriptions for grammars stored in grammar cache.
If we have DTD-based DITA topics located in different folders using public IDs to refer to the DTDs the parser should be able to re-use the DTD grammars between them.

Signed-off-by: Radu Coravu radu_coravu@sync.ro

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name: Pull request
about: Propose changes to fix an issue or implement a new feature

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Description

Motivation and Context

How Has This Been Tested?

Type 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 changes existing functionality)

Documentation and Compatibility

• What documentation changes are needed for this feature?
  (Provide links to existing documentation topics that will require updates)
• Will this change affect backwards compatibility or other users' overrides?

Checklist

• My code follows the code style of this project.
  • https://github.com/dita-ot/dita-ot/wiki/Java-Coding-Conventions
  • https://github.com/dita-ot/dita-ot/wiki/XSLT-Coding-Conventions
  • https://github.com/dita-ot/docs/wiki/coding-guidelines
• I have updated the unit tests to reflect the changes in my code.