Add support for configurable warnings (backport #3414)

[mergify]

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Changes to be committed:
	modified:   core/src/main/scala/chisel3/ChiselEnum.scala
	modified:   core/src/main/scala/chisel3/experimental/SourceInfo.scala
	modified:   core/src/main/scala/chisel3/experimental/hierarchy/core/Definition.scala
	modified:   core/src/main/scala/chisel3/internal/Builder.scala
	modified:   core/src/main/scala/chisel3/internal/Error.scala
	new file:   core/src/main/scala/chisel3/internal/Warning.scala
	modified:   core/src/main/scala/chisel3/internal/firrtl/Converter.scala
	new file:   docs/src/explanations/warnings.md
	modified:   src/main/scala/chisel3/aop/injecting/InjectingAspect.scala
	modified:   src/main/scala/chisel3/stage/ChiselOptions.scala
	modified:   src/main/scala/chisel3/stage/phases/Elaborate.scala
	modified:   src/test/scala/chisel3/testers/TestUtils.scala
	new file:   src/test/scala/chiselTests/stage/WarningConfigurationSpec.scala

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	both modified:   core/src/main/scala/chisel3/Aggregate.scala
	both modified:   core/src/main/scala/chisel3/Bits.scala
	both modified:   core/src/main/scala/chisel3/internal/package.scala
	both modified:   docs/src/explanations/explanations.md
	both modified:   src/main/scala/chisel3/stage/ChiselAnnotations.scala
	both modified:   src/main/scala/chisel3/stage/package.scala
	both modified:   src/main/scala/circt/stage/ChiselStage.scala
	deleted by us:   src/test/scala/chiselTests/ConstSpec.scala
	deleted by us:   src/test/scala/chiselTests/ProbeSpec.scala
	both modified:   website/docs/src/main/resources/microsite/data/menu.yml

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Original PR Body

Currently opened as a draft but I would like to get the ball rolling on this.

This is heavily inspired by configurable warnings in Scala, but is a little more limited.

TODO

• Audit warning numbering (want to backport to 3.6, so make sure warnings existing there are first in order)
• Add warning number to warning messages
• Make new warnings more clear that they are deprecations I'm going to do this in a follow on PR
• Write a docs page
• Write release notes
• Add support for --warn-conf-file which is the same syntax but with \n separated pairs in a file rather than , separated pairs in a String.
• Add tests mixing --warn-conf-file with --warn-conf

The commit text gives a pretty good overview:

Add support for configurable warnings

Warnings have been assigned unique integers to use as identifiers for
purposes of documentation and configuration.

New CLI option --warn-conf accepts a comma-separated sequence of
<filter>:<action> pairs for customizing warnings.

Supported filters are:
* any          - matches all warnings
* id=<integer> - matches warnings with the integer id
* src=<glob>   - matches warnings where <glob> matches the warning
                 source file

id and src filters can be combined with &.

Supported actions are:
* :s - suppress the warning
* :w - report the warning as a warning (default behavior)
* :e - error on the warning

For example, the new Vec dynamic width matching warning can be
suppressed for source files in src/main/scala while all other warnings
elevated to errors with:
  --warn-conf "id=4&src=src/main/scala/**:s,any:e"

The is also --warn-conf-file which works similarly to --warn-conf except
the <filter>:<action> pairs are newline separated in a file. # is used
for line comments.

Contributor Checklist

• Did you add Scaladoc to every public function/method?
• Did you add at least one test demonstrating the PR?
• Did you delete any extraneous printlns/debugging code?
• Did you specify the type of improvement?
• Did you add appropriate documentation in docs/src?
• Did you request a desired merge strategy?
• Did you add text to be included in the Release Notes for this change?

Type of Improvement

• Feature (or new API)

Desired Merge Strategy

• Squash

Release Notes

Add support for configurable warnings, see https://www.chisel-lang.org/chisel3/docs/explanations/warnings.html

Reviewer Checklist (only modified by reviewer)

• Did you add the appropriate labels? (Select the most appropriate one based on the "Type of Improvement")
• Did you mark the proper milestone (Bug fix: 3.5.x, 3.6.x, or 5.x depending on impact, API modification or big change: 6.0)?
• Did you review?
• Did you check whether all relevant Contributor checkboxes have been checked?
• Did you do one of the following when ready to merge:
  • Squash: You/ the contributor Enable auto-merge (squash), clean up the commit message, and label with Please Merge.
  • Merge: Ensure that contributor has cleaned up their commit history, then merge with Create a merge commit.

[jackkoenig]

If we ever merge this, include the typo fix in #4029

Nevermind, that warning doesn't exist in 3.6