Mass deprecations, to be removed in Chisel 7 (backport #4754)

[chiselbot]

Mass deprecation of APIs that we would like to delete in Chisel 7.

Release Notes

• Deprecate FileUtils
• Deprecate BlackBoxResourceFileNameAnno
• Deprecate BlackBoxSourceHelper
• Deprecate BackendCompilationUtilities

  ---

  This is an automatic backport of pull request Mass deprecations, to be removed in Chisel 7 #4754 done by Mergify.

[mergify]

Cherry-pick of 868c195 has failed:

On branch mergify/bp/6.x/pr-4754
Your branch is up to date with 'origin/6.x'.

You are currently cherry-picking commit 868c1958.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   firrtl/src/main/scala/firrtl/FileUtils.scala
	modified:   firrtl/src/main/scala/firrtl/transforms/BlackBoxSourceHelper.scala
	modified:   firrtl/src/main/scala/firrtl/util/BackendCompilationUtilities.scala

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   firrtl/src/test/scala/firrtlTests/FileUtilsSpec.scala
	both modified:   src/test/scala/chiselTests/Harness.scala

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally