Create a new `IRBuilderBase::CreateAllocationSize` method to compute the
runtime size of an alloca as a Value*. This handles both static and
dynamic allocas by computing `ArraySize * ElementSize`, and using
CreateTypeSize to properly handle scalable vectors.
This de-duplicates code across multiple instrumentation and analysis
passes and increases consistency.
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
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