[ExtractAPI] Add support for anyAppleOS (#197929)
6c8940ccad31457aadb48c6f2bce139b1c5dda01 introduced support for
anyAppleOS, which can be used to indicate availability for all Apple
platforms in a single availability attribute.
3089120f0cd2fe78911d1bc9703764a07fa7eb32 updated it to preserve the
original attribute info and store the inferred platform-specific
attribute in a separate field which, if present, is returned by
`getEffectiveAttr()`.
With these changes, ExtractAPI now reports these availabilities verbatim
for an "anyAppleOS" platform as the availability info for Decls directly
uses the availability attribute without fetching the effective
attribute. The expected output would be the target platform for which
the symbol graph is being built. This patch updates the availability
collection logic to use `getEffectiveAttr()` and include the target
platform instead of "anyAppleOS" for symbol availabilities in symbol
graphs.
rdar://174558184
