Make rules_java backwards compatible with Bazel 6.3.0

Copybara Import from https://github.com/bazelbuild/rules_java/pull/210

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Make rules_java backwards compatible with Bazel 6.3.0 (#210)

Move bootstrap_toolchain_type into rules_java. There are no uses outside
of rules_java. This fixes compatiblity with Bazel 6.3.0, which doesn't
have the definition.

Add back `_allowlist_function_transition`. Older versions of Bazel require it.

Add Bazel 6.3.0 to the CI.

Remove a couple of broken targets from toolchains/BUILD. Those were
broken becuase old JDKs were removed.

Closes #210
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COPYBARA_INTEGRATE_REVIEW=https://github.com/bazelbuild/rules_java/pull/210 from comius:backward-compatible-rules_java 393f270312cbb13fa5bc7807b93cf95f1e7b3969
PiperOrigin-RevId: 670415171
Change-Id: I7f42cc92bb7285cb51a2a1185695451a644d5b30