[FR] regex substitution support in expand_template

[peakschris]

It would be very helpful to be able to match using regex in expand_template:

expand_template(
  regex_substitutions = {
      "^whole_line$": "replace_whole_line"
      "capture (\w+) something": "use $1 in a replacement"
      "^delete_line$\n": ""
  }
)

It seems like a fairly straightforward implementation given https://github.com/bazel-contrib/bazel-lib/blob/main/tools/expand_template/main.go already exists; we would always use this engine when regex_substitutions was set.

We could contribute this; would it be welcome?

Thanks!