Support for incremetal platform prebuilt APIs

This change provides support for prebuilt incremental platform API (i.e.
API changes associated with a QPR, as opposed to a major dessert
releas).

This feature is provided via the existing prebuilt_apis module with the
introduction of a new attribute:

    allow_incremental_platform_api

While typical platform prebuilt APIs are presumed to be under a
directory structure that follows the pattern:

<version>/<scope>/<module>.jar
<version>/<scope>/api/<module>.txt

Where <version> is limited to a single integer signifying the API level.

For modules where allow_incremental_platform_api is set to 'true' (false
by default) the pattern is the same, however <version> is presumed to be
of the form MM.m, where MM aligns with the existing API level and m
signifies the incremental release (e.g. QPR).

Bug: b/280790094
Test: platform build check with both incremental & non-incremental API
      cd build/soong && go test ./java
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:eee6995093485497bc29cdce01c2a86765ffb4eb)
Change-Id: I67e293006ccfa210d0dcc0a294db894632f1b6cb