fix: reduce false positives from local variable shadowing and early-return guards

[Akshay090]

Fixes #688

Summary

Two related fixes that reduce false positives in the compat/compat rule:

1. Function parameter names matching browser APIs

The Identifier visitor that tracks locally declared names was missing ArrowFunctionExpression and FunctionExpression parent types. This caused false positives when callback parameters happened to share a name with a browser API.

Example — flagged incorrectly before this fix:

// 'scheduler' here is a domain entity, not the Window.scheduler browser API
schedulers.map(scheduler => scheduler.name);

The existing heuristic already handled FunctionDeclaration params, VariableDeclarator, Property, ClassDeclaration, and import specifiers. This adds the two missing function types for consistency.

2. Early-return guard pattern as feature detection

The existing isInsideIfStatement heuristic only suppressed errors for API usage inside an if block. The common early-return guard pattern was missed:

function setup() {
  if (!('serviceWorker' in navigator)) { return; }
  navigator.serviceWorker.register('/sw.js'); // was falsely flagged
}

The new isGuardedByEarlyReturn helper walks up from the flagged node to its containing block and checks preceding sibling if-statements for early exits (return/throw) whose test references the same API. Respects the ignoreConditionalChecks setting.

Test plan

• Added 4 valid test cases for arrow function and function expression parameter shadowing
• Added 4 valid test cases for early-return guard patterns (in operator, member expression, throw, bare identifier)
• Added 2 invalid test cases (unrelated guard doesn't suppress; ignoreConditionalChecks overrides early-return detection)
• All 118 tests pass, lint clean, build succeeds