[LLVM][ARM] Add native ct.select support for ARM32 and Thumb

This patch implements architecture-specific lowering for ct.select on ARM
(both ARM32 and Thumb modes) using conditional move instructions and
bitwise operations for constant-time selection.

Implementation details:
- Uses pseudo-instructions that are expanded Post-RA to bitwise operations
- Post-RA expansion in ARMBaseInstrInfo for BUNDLE pseudo-instructions
- Handles scalar integer types, floating-point, and half-precision types
- Handles vector types with NEON when available
- Support for both ARM and Thumb instruction sets (Thumb1 and Thumb2)
- Special handling for Thumb1 which lacks conditional execution
- Comprehensive test coverage including half-precision and vectors

The implementation includes:
- ISelLowering: Custom lowering to CTSELECT pseudo-instructions
- ISelDAGToDAG: Selection of appropriate pseudo-instructions
- BaseInstrInfo: Post-RA expansion of BUNDLE to bitwise instruction sequences
- InstrInfo.td: Pseudo-instruction definitions for different types
- TargetMachine: Registration of Post-RA expansion pass
- Proper handling of condition codes and register allocation constraints