Fix up @build_tools//tools/java package

bazelbuild#12994 added the file, but it's
currently exposed as:
`@build_tools//tools:java/java_stub_template.txt`

This fixes it up to be properly exposed as:
`@build_tools//tools/java:java_stub_template.txt`

Which makes more sense :)

tools/java/BUILD

@@ -19,8 +19,21 @@ genrule(
     visibility = ["//tools:__pkg__"],
 )
 
+# Generate a BUILD.bazel file to put in the repo, as this one references targets which don't exist in a Bazel distribution.
+# Note: We need to call it BUILD.bazel not BUILD because otherwise it conflicts with this file.
+genrule(
+    name = "generated_BUILD",
+    srcs = ["BUILD.for_buildtools"],
+    outs = ["BUILD.bazel"],
+    cmd = "cp $< $@",
+)
+
 filegroup(
     name = "embedded_tools",
-    srcs = ["//tools/java/runfiles:embedded_tools"],
+    srcs = [
+        ":generated_BUILD",
+        ":java_stub_template.txt",
+        "//tools/java/runfiles:embedded_tools",
+    ],
     visibility = ["//tools:__pkg__"],
 )

tools/java/BUILD.for_buildtools

@@ -0,0 +1 @@
+exports_files(["java_stub_template.txt"])