[red-knot] Add symbols defined by match statements

[dhruvmanila]

Summary

This PR adds symbols introduced by match statements.

There are three patterns that introduces new symbols:

• as pattern
• Sequence pattern
• Mapping pattern

The recursive nature of the visitor makes sure that all symbols are added.

Test Plan

Add test case for all types of patterns that introduces a symbol.

[codspeed-hq]

CodSpeed Performance Report

Merging #12926 will not alter performance

_{Comparing dhruv/match-stmt-symbols (c08d870) with main (aefadde)}

Summary

✅ 32 untouched benchmarks

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

[carljm]

Looks great!