[SPIRV] Emit DebugLexicalScope for forloop controls (#8514)

[SteveUrquhart]

Adds missing DebugLexicalScope to for-loops, fixes #8514

[damyanp]

/azp run

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[Copilot]

Pull request overview

This PR updates the SPIR-V emitter’s rich debug info generation to introduce an additional lexical scope for for loop controls (the for (<init>; <cond>; <inc>) region), addressing missing scope nesting reported in #8514 and updating FileCheck expectations accordingly.

Changes:

• Emit an extra DebugLexicalBlock for for loop controls and push/pop it during ForStmt emission.
• Update rich debug scope expectations so %for_check, %for_continue, and %for_merge use the new controls lexical scope.
• Refresh DebugLexicalBlock expectations in related SPIR-V debug-info tests (line/column and parent-scope relationships).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
tools/clang/test/CodeGenSPIRV/shader.debug.debuglexicalblock.hlsl	Updates NS100 debug lexical block expectations to include a separate for controls lexical scope.
tools/clang/test/CodeGenSPIRV/rich.debug.debugscope.hlsl	Updates rich debug scope expectations for for blocks/labels to reference the new controls scope.
tools/clang/test/CodeGenSPIRV/rich.debug.debuglexicalblock.hlsl	Updates rich debug lexical block expectations to include the new for controls lexical scope.
tools/clang/lib/SPIRV/SpirvEmitter.cpp	Adds push/pop of a new debug lexical scope around for loop emission when rich debug info is enabled.

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