Don't create a subpath for extracted_srcjar

[antonsviridov-src]

Closes GRAPH-988

This avoids an issue where we declare output to be a prefix of the rule's own outputs:

testing_test                           (prefix)
testing_test/extracted_srcjar/...      (longer path starting with prefix)

Doesn't seem like it was necessary to use nesting, as long as the output name contains both the source jar path, and the task name.

Here's the original error from Bazel (formatting mine, you just now Bazel doesn't output no newlines or structure...):

ERROR: 
     output path 'bazel-out/darwin_arm64-fastbuild/bin/src/main/java/srcjar_example/testing_test' 
     (belonging to //src/main/java/srcjar_example:testing_test) 
is a prefix of 
     output path 'bazel-out/darwin_arm64-fastbuild/bin/src/main/java/srcjar_example/testing_test/extracted_srcjar/src/main/java/srcjar_example/sources.srcjar' 
     (belonging to //src/main/java/srcjar_example:testing_test). 

These actions cannot be simultaneously present; please rename one of the output files or build just one of them

Test plan

Added a test case from #757