Add add_opens and add_exports support

[timothyg-stripe]

JDK 17 strongly encapsulates JDK internals, so many libraries need --add-opens= and --add-exports= JVM flags. Bazel's Java rules support adding those flags through java_library(add_opens = [...], add_exports = [...]), and these fields are read in Bazel's java_binary rule:

https://github.com/bazelbuild/bazel/blob/a2d3f20b577b8b5c7c5027a8a00f8c24a66228b9/src/main/starlark/builtins_bzl/common/java/java_binary.bzl#L173-L182

However it appears that the rules_scala doesn't read those fields when filling out the executable template:

rules_scala/scala/private/phases/phase_write_executable.bzl

Line 106 in 421a9e8

jvm_flags = " ".join(

Additionally, it would be nice if scala_library, scala_binary, and scala_import support add_opens and add_exports attributes also, but it's not as urgent as the first issue.

[timothyg-stripe]

See bazelbuild/bazel#20033 on a Bazel-side blocker for Scala rules to have add_exports / add_opens attributes.