fix(RF01): support parenthesized joined tables in FROM clause

[benfdking]

Summary

Fixes #1573

This PR adds support for parsing and analyzing parenthesized joined tables in FROM clauses, such as:

SELECT c.id, ci.id
FROM users AS u
CROSS JOIN (
    course_instances AS ci
    JOIN pl_courses AS c ON c.id = ci.course_id
)
LEFT JOIN enrollments AS e ON e.user_id = u.user_id

Previously, sqruff would fail to parse the parenthesized join expression and the RF01 rule would incorrectly report that table aliases like c and ci were not found in the FROM clause.

Changes

• Add JoinTargetGrammar in ANSI dialect that allows either:
  • FromExpressionElementSegment (simple table)
  • Bracketed(FromExpressionSegment) (parenthesized joined tables)
• Update JoinClauseSegment to use JoinTargetGrammar instead of FromExpressionElementSegment
• Update JoinClauseSegment::eventual_aliases() to extract table aliases from bracketed FromExpression segments
• Add test case for the reported issue

Test plan

• Verified the SQL from the issue now parses correctly
• Verified RF01 no longer reports false positives for table aliases inside parenthesized joins
• Ran cargo clippy and cargo fmt
• Existing dialect tests pass

🤖 Generated with Claude Code

[github-actions]

Benchmark for cdbba8b

Click to view benchmark

Test	Base	PR	%
DepthMap::from_parent	52.7±0.68µs	52.2±1.45µs	-0.95%
fix_complex_query	12.4±0.15ms	12.3±0.12ms	-0.81%
fix_superlong	189.8±7.53ms	186.4±10.64ms	-1.79%
parse_complex_query	4.1±0.03µs	4.2±0.05µs	+2.44%
parse_expression_recursion	7.1±0.09µs	7.2±0.12µs	+1.41%
parse_simple_query	1043.1±10.29ns	1052.4±20.72ns	+0.89%

[github-actions]

Benchmark for b62b564

Click to view benchmark

Test	Base	PR	%
DepthMap::from_parent	52.1±0.51µs	51.8±0.66µs	-0.58%
fix_complex_query	12.3±0.46ms	12.3±0.10ms	0.00%
fix_superlong	156.9±4.22ms	164.4±11.59ms	+4.78%
parse_complex_query	4.2±0.08µs	4.2±0.04µs	0.00%
parse_expression_recursion	7.2±0.10µs	7.1±0.10µs	-1.39%
parse_simple_query	1043.2±16.53ns	1073.3±11.70ns	+2.89%