Move legacy-test to test-base

Make it consistent with the test-mock and test-runner directories.
Also renames the files in api/ subdirectory.

(cherry picked from commit f779efd62cd579f67bd3b387d59fda11ee0cbe90)

Bug: 30188076
Test: make checkbuild
Change-Id: Ied3621e6201d8717223fe1ccd4ea77d458126b25
Merged-In: If4f99a65fcca416ede5b3e63481398f0b451bcb7
diff --git a/Android.mk b/Android.mk
index 2d74249..cf6aa2a 100644
--- a/Android.mk
+++ b/Android.mk
@@ -82,7 +82,7 @@
 # to document and check apis
 files_to_check_apis := \
   $(call find-other-java-files, \
-    legacy-test/src \
+    test-base/src \
     $(non_base_dirs) \
   )