CtsSaxTestCases: Run for all libcore changes.

This CL achieves that my moving TEST_MAPPING to the root folder.

The reason we want to run it for changes outside javax.xml is that
such changes might break CtsSaxTestCases (rare, but possible). atest
takes 20sec to run the test, but the actual test execution completes
in milliseconds. At 20sec/run, this would amount to about 10h of
Treehugger time over a year with 600 CLs x 3 Treehuggr runs/CL).

Test: croot libcore && atest

Change-Id: Ied2366d1d0fedce77262eeeecd03d657e4401e83
1 file changed