[water] introduce WaveSymbolMappingAttr

[ftynse]

This is a dedicated attribute usable as a nearly drop-in replacement for a dictionary attribute of expression lists. It uses WaveSymbolAttr instances as keys instead of strings and by design preserves the order in which keys appear.

Usage of this attribute will be introduced progressively in separate commits.

Partially supersedes #730

[Copilot]

Pull request overview

Introduces WaveSymbolMappingAttr, a new ordered mapping attribute for the Wave dialect that maps WaveSymbolAttr keys to WaveExprListAttr values while preserving insertion order (intended as an ordered alternative to dictionary-based attributes). It also adds a small test-only op and MLIR tests to validate printing/parsing, ordering, and verifier behavior.

Changes:

• Add WaveSymbolMappingAttr definition (TableGen) plus custom parse/print, verification, and helper APIs (verifyResultCount, lookup).
• Add water_test.wave_symbol_mapping test op with a verifier that checks a uniform result count across mapped expr lists.
• Add positive/negative MLIR tests for parsing/printing, ordering preservation, duplicate keys, and result-count verification.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
water/include/water/Dialect/Wave/IR/WaveAttrs.td	Declares WaveSymbolMappingAttr and its public helper methods.
water/lib/Dialect/Wave/IR/WaveAttrs.cpp	Implements custom assembly format parsing/printing and verification for the new attribute.
water/test/lib/Dialect/WaterTestDialect.td	Adds a dummy op to hold/verify WaveSymbolMappingAttr in tests.
water/test/lib/Dialect/WaterTestDialect.cpp	Implements the dummy op verifier using verifyResultCount.
water/test/Dialect/Wave/attr-type.mlir	Adds roundtrip/ordering tests for #wave.symbol_mapping.
water/test/Dialect/Wave/attr-type-invalid.mlir	Adds negative tests for duplicate keys and mismatched expr_list result counts.

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[martin-luecke]

Nothing really to add beyond what copilot wrote.
IMO this could have been combined with #928

[ftynse]

IMO this could have been combined with #928

#930 is based on this but does not require #928, which allows for better staging if generalization ends up being problematic / needing deeper changes to address review

[ftynse]

Numeric issue is irreleavnt