Add BTI support to MLAS AArch64 assembly (#32070)
## Description
Add Branch Target Identification support to MLAS AArch64 assembly when
the compiler enables __ARM_FEATURE_BTI_DEFAULT.
- emit BTI C landing pads at exported assembly function entries
- emit the ELF GNU_PROPERTY_AARCH64_FEATURE_1_BTI note
- cover both conventional MLAS assembly macros and generated portable
SVE assembly
- preserve output for builds without BTI enabled
This allows Android consumers to link MLAS objects with -z force-bti
without disabling BTI hardening.
## Validation
- ONNX Runtime lintrunner passes for all changed files
- all 29 MLAS AArch64 assembly files cross-assemble with
-mbranch-protection=standard
- all 29 resulting objects advertise AArch64 feature: BTI
- conventional and generated SVE entries begin with BTI C only when BTI
is enabled
- all 29 objects link successfully with LLD --fatal-warnings -z
force-bti
