Refactor readobj to integrate AArch64 Build Attributes under
ELFAttributeParser. ELFAttributeParser now serves as a base class for:
- ELFCompactAttrParser, handling Arm-style attributes with a single
build attribute subsection.
- ELFExtendedAttrParser, handling AArch64-style attributes with multiple
build attribute subsections. This improves code organization and better
aligns with the attribute parsing model.
Add support for parsing AArch64 Build Attributes.
The de-facto convention for build attributes file and class names seems
to be 'Attrs' in the class name and 'Attributes' in the file name.
Accordingly, change file ARMBuildAttrs.cpp -> ARMBuildAttributes.cpp And
class AArch64BuildAttrs --> AArch64BuildAttributes
