GH-50995: [C++][Compute] Support mixed StringView and BinaryView comparison

[Jay846]

Rationale for this change

This PR adds comprehensive cross-type comparison support for StringView and BinaryView types against standard offset-based string/binary layout containers across all 6 core comparison operators.

What changes are included in this PR?

• Universal Operator Dispatches: Extended internal dispatches in codegen_internal.cc to map mixed string configurations cleanly across all six relational operators (equal, not_equal, greater, greater_equal, less, less_equal).
• Offset Bounds Safety: Configured view parsing parameters to cleanly unpack both inline arrays and out-of-line data buffers handling boundaries exceeding the 12-byte baseline optimization limit.

Are these changes tested?

Yes, added dedicated hierarchical test suites inside scalar_compare_test.cc verifying:

• MixedTypesNullPropagation: Confirms valid null mapping across disjoint array inputs.
• MixedTypesAllOperators: Programmatic testing matrix validating all relational operators.
• MixedTypesBoundaryAndSlices: Ensures non-zero pointer slices evaluate without indexing out-of-bound errors.

• GitHub Issue: [C++][Compute] Support comparison kernels for mixed StringView/BinaryView and standard Binary/String types #50995

[github-actions]

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See also:

• Other pull requests
• Contribution Guidelines - Contributing Overview

[github-actions]

⚠️ GitHub issue #50995 has been automatically assigned in GitHub to PR creator.