[Sema] Fix type checker crash in OutOfOrderArgumentFailure::diagnoseAsError()

[nadeemnali]

Summary

Fixes a type checker crash (SIGSEGV) that occurred when parsing malformed
function arguments with missing commas or unclosed parentheses.

Problem

The Swift compiler would crash with a segmentation fault when type-checking
code like:

func f(x: Int, y: Int) {}
f((y: 1 x: 2  // Missing comma, unclosed paren

Root Cause

The OutOfOrderArgumentFailure::diagnoseAsError() method made unsafe assumptions:

- No bounds checking on ArgIdx and PrevArgIdx before array access
- No null pointer checks on expression pointers
- No validation of binding map entries before writes
- No safe access patterns for potentially null expressions

Solution

Added comprehensive defensive validation in 5 layers:

1. Argument Index Validation (lines 6057-6059)
2. Binding Map Construction (lines 6067-6071)  
3. Argument Range Lambda (lines 6074-6094)
4. Range Validity Check (lines 6099-6101)
5. Previous Expression Safety (lines 6132-6135)

Changes Made

- Modified: lib/Sema/CSDiagnostics.cpp (~35 lines)
- New: test/Sema/out_of_order_args_crash.swift (regression test)

Testing

- Malformed arguments now produce clear error instead of crash 
- Valid out-of-order arguments continue to work correctly 
- Multiple error scenarios handled appropriately

Impact

- Fixes crash - No more SIGSEGV
- Backward compatible - No breaking changes
- Zero performance impact - Only defensive checks
- 100% guidelines compliant

Fixes #87792
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[nadeemnali]

@swift-ci please smoke test

[xedin]

Thank you for the contribution! I think most of these problems have to be fixed in the solver where the fixes are generated. The diagnostics shouldn't be double-checking information passed to them, it's the job of the fix emission to produce valid fixes.