Release Catch3 0.3.0.2

Carry mocks in the amalgamated files

repo_info starts Git in the checkout with fixed commands, so a shell never
reads a path, reports an unknown state as null rather than clean, and
counts only files it can start. third_party reads every archive before
it changes a file and refuses two modes. version checks that the sources
make a distribution, computes every place before writing any, and
release_notes finds a three-number heading for a version with D = 0.

Install again with CMake

The scripts in use become programs run with `bazelisk run //tools:<tool>`,
and arguments follow `--`:

  amalgamate     the single-file distribution; --check only compares it
  check          licenses, convenience headers, header guards, file names,
                 versions and whether the distribution is up to date
  third-party    compares third_party/ with its archives, or writes it
  version        prints the version, or moves every place that states it
  release-notes  prints a section of the release notes
  repo-info      reports the checkout and the tools on PATH; --json writes
                 it through yyjson, with the fields of Tala's repo-info

amalgamate writes what the Python script wrote, byte for byte, except for
the time of generation. That line is gone so that the output is
deterministic and --check can compare it.

MODULE.bazel now pins the archives of third_party/ by version and sha256,
so Bazel fetches and checks them instead of a tool of ours, and Renovate
reads the versions there.

Scripts nobody used are gone: fixWhitespace, updateDocumentSnippets,
buildAndTest, and updateDocumentToC, which rewrote unrelated documents.
CheckConvenienceHeaders leaves CTest, since //tools:check runs it in CI.
The Python of tests/TestScripts stays: those are tests, not tools.

Mock.hpp goes into catch_amalgamated.hpp, since tests use it directly, and
Mock.cpp into catch_amalgamated.cpp. The test of the amalgamated files
now uses a mock, so a file left out fails it.