[CIR][X86] Add MSVC bit scan builtins (#234304)
## Summary
Add CIR code generation support for the MSVC X86 bit-scan intrinsics:
- `_BitScanForward`
- `_BitScanReverse`
- `_BitScanForward64`
- `_BitScanReverse64`
The implementation:
- Uses `cir.ctz` for forward scans.
- Uses `cir.clz` to calculate the highest set-bit index for reverse
scans.
- Writes the result index only when the input mask is non-zero.
- Returns the expected boolean success value.
- Supports both 32-bit and 64-bit masks.
## Tests
Add CIR FileCheck tests covering all four intrinsics and verifying the
generated zero checks, scan operations, conditional stores, casts, and
return values.
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Co-authored-by: Nayan112 <nayan.modak.2006@gmail.com>
Co-authored-by: dwbh21 <anant.maheshwary@gmail.com>
