AIDL API check ignores blank lines and comments

The API signature file now contains warning preamble as comments. The
comments shouldn't fail 'diff'.

Bug: 134452637
Test: m out/soong/.intermediates/frameworks/base/services/net/ipmemorystore-aidl-interfaces-api/checkapi_dump.timestamp
with ag/7952481 applied in qt-dev.

Merged-In: I5547b768c216ee67e7d2d3b82752a94fea27004c
(cherry picked from commit 8558309645adf15978321528b71a60e45731a250)

Change-Id: I5547b768c216ee67e7d2d3b82752a94fea27004c
1 file changed