Gazelle tolerates common errors, which is fine for daily uses.
However when being used for scripting, we will need a way to
tell if such errors have occored. This CL adds -strict flag
to exit with non-zero value after seeing those errors.

* upstream/master:
  fix: Remove gazelle_binary import collision (bazelbuild#1226)
  Update extend.md with a practical languages example (bazelbuild#1222)
  Add test of diff mode
  Add e2e test for normal operations
  Make `gazelle_generation_test`'s take a list
  Add instructions on regenerating `go_repository_tools_srcs.bzl`
  fix(tests): fix gazelle_generation_test expected stderr update (bazelbuild#1220)

* upstream/master:
  gazelle_generation_test: redact workspace path from output
  Broaden label name regex (bazelbuild#1229)

* upstream/master:
  Add -print0 to print names of rewritten files (bazelbuild#1213)