Set up Verible lint and format tests with Bazel; bring up `@rules_hdl`

[mgottscho]

• [X] Write new rules
  • verible_lint_test
  • verible_format_test
• [X] Write new macro
  • verible_test - expands to lint test and format test
• [X] Fix lint and format issues in sources
• [X] Copy over bazel stuff from https://github.com/google/xls (Apache 2.0-licensed) for getting @rules_hdl to work
  • (Needed for verilog_library targets that we will be using soon)
  • Retained original XLS copyright notices, and added comments to indicate when the original file had been changed.
• [X] Update README.adoc

Future work outlined in //bazel:verible.bzl:

# TODO(mgottscho): The lint and format rules here are not the ideal solution.
# We'd prefer to only run the linter and formatter on the changed lines in a
# git diff so that we can change the lint/format rules over time (if needed)
# and have the tests gradually ratchet over the codebase. I'm fine with this
# non-ideal solution for now, though, since we're setting this up on a fresh
# codebase and moving fast.
#
# The ideal solution would probably look like this:
#
# bazel run //:verible-format      # Test only changed lines
# bazel run //:verible-format-fix  # Test and fix changed lines in-place
#
# bazel run //:verible-format -- <file1.sv> <file2.sv>  # Run on specific files
# bazel run //:verible-format-fix -- <file1.sv> <file2.sv>  # Fix specific files
#
# bazel run //:verible-format -- --all      # Test all lines
# bazel run //:verible-format-fix -- --all  # Fix all lines