Rename BuildDir and NinjaBuildDir.

These are just out/ and out/soong/ and the old names were quite
confusing.

Test: Presubmits.
Change-Id: I999ca62162062f27e449f83ffb00fa580d4065b8
diff --git a/java/base.go b/java/base.go
index ea5b137..416d82a 100644
--- a/java/base.go
+++ b/java/base.go
@@ -793,7 +793,7 @@
 			// Manually specify build directory in case it is not under the repo root.
 			// (javac doesn't seem to expand into symbolic links when searching for patch-module targets, so
 			// just adding a symlink under the root doesn't help.)
-			patchPaths := []string{".", ctx.Config().BuildDir()}
+			patchPaths := []string{".", ctx.Config().SoongOutDir()}
 
 			// b/150878007
 			//