[Build Attributes] Standardize names according to convention. (#124556)

The de-facto convention for build attributes file and class names seems
to be 'Attrs' in the class name and 'Attributes' in t

[Build Attributes] Standardize names according to convention. (#124556)

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

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