Centralize a couple JIT arithmetic helpers

[tannergooding]

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[Copilot]

Pull request overview

This PR refactors a few low-level JIT bit-manipulation helpers to use the shared BitOperations implementation instead of maintaining local counting/log2 helpers. It keeps the change scoped to internal helper code used by JIT bitsets and hash bit-vectors.

Changes:

• Replaced hashbv’s local nearest_pow2 and word-popcount helpers with BitOperations::Log2/PopCount.
• Replaced BitSetSupport::CountBitsInIntegral call sites in the UINT64 and ShortLong bitset implementations with BitOperations::PopCount.
• Removed the now-unused BitSetSupport nibble-count table and integral bit-count helper implementation.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/coreclr/jit/hashbv.h	Swaps nearest_pow2 over to BitOperations::Log2.
src/coreclr/jit/hashbv.cpp	Replaces local hashbv popcount helpers with shared BitOperations::PopCount.
src/coreclr/jit/bitsetasuint64.h	Uses shared popcount for the UINT64 bitset representation.
src/coreclr/jit/bitsetasshortlong.h	Uses shared popcount for both short and long BSShortLong counting paths.
src/coreclr/jit/bitset.h	Removes obsolete integral bit-count helper declarations.
src/coreclr/jit/bitset.cpp	Removes obsolete nibble-count lookup table definition.

[tannergooding]

CC. @dotnet/jit-contrib, small cleanup as I noticed we had a couple remaining custom popcount algorithms, so I fixed them to just forward to the utils.h implementation instead.

There is a small annoying bit where size_t for Apple is neither uint32_t nor uint64_t (rather it is unsigned long, rather than unsigned int or unsigned long long) and is "ambiguous" between the two, but then it conflicts with them on other targets

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.