base_rules.mk: Copy LOCAL_TEST_DATA to testcase folders.

* Moves the test data logic up to before suite logic.
* Saves the source to relative dest pairs.
* Re-uses the saved source to relative dest pairs when generating
  the src:dst pairs for suites.

Bug: 69802886
Test: Build a native test with test data and ensured test data
      ended up in each arch specific destination folder.

Change-Id: I52cf8771487fb52276f5e6aae5b8eecb222544d7