NDK library: collect NDK headers for ABI monitoring

Collect all NDK exported headers paths into a file that is used to
detect public types that should be ABI monitored.

Assume that we have the following code in exported header:

typedef struct Context Context;
typedef struct Output {
    ...
} Output;
void DoSomething(Context* ctx, Output* output);

If none of public headers exported to end-users contain definition of
"struct Context", then "struct Context" layout and members shouldn't be
monitored. However we use DWARF information from a real library, which
may have access to the definition of "string Context" from
implementation headers, and it will leak to ABI.

STG tool doesn't access source and header files, only DWARF information
from compiled library. And the DWARF contains file name where a type is
defined. So we need a rule to build a list of paths to public headers,
so STG can distinguish private types from public and do not monitor
private types that are not accessible to library users.

Bug: 156513478
Test: development/tools/ndk/update_ndk_abi.sh with enabled canDumpAbi
Change-Id: I9fa41e73450a41379638debb3dc56f421e0fb870
Signed-off-by: Aleksei Vetrov <vvvvvv@google.com>