__INTRODUCED_IN macros add the availability attribute

__INTRODUCED_IN (and its variants) macro is used to mark the
availability of an API symbol. The macros were used by the versioner
tool for the NDK clients. When the Bionic headers are processed by the
tool, APIs with the macros are guarded with __ANDROID_API__. e.g.,

void foo() __INTRDUCED_IN(30);

is processed into

\#if __ANDROID_API__ >= 30
void foo();
\#endif

by the versioner.

The macros however didn't play a role for other cases, e.g. OS
components.

This is too strict for NDK clients and too loose for the non-NDK
clients. For the former, this completely hides the APIs that are newer
than the min sdk version (__ANDROID_API__). For the latter, a call to
such an API can be made without being guarded.

This change is the first step towards a better way of handling the
native APIs availability. The plan is that every NDK APIs are annotated
with the availability attribute and callers are required to guard their
API calls with a runtime check if the API is newer than the min sdk
version of the caller.

In this change, the macros now emits the availability attribute for the
non-NDK clients (i.e. when not processed by versioner).

Bug: 163288375
Bug: 134795810
Test: m
Change-Id: I6eb2bce2bc2770cbfd69815e6816b6f25b3d6127

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