Support literals and DontCare in DataView targets (backport #3389)

[mergify]

This is an automatic backport of pull request #3389 done by Mergify.
Cherry-pick of 0f803cd has failed:

On branch mergify/bp/5.x/pr-3389
Your branch is up to date with 'origin/5.x'.

You are currently cherry-picking commit 0f803cd87.
  (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:   core/src/main/scala/chisel3/experimental/dataview/package.scala

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   src/test/scala/chiselTests/experimental/DataView.scala

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

---

Mergify commands and options

More conditions and actions can be found in the documentation.

You can also trigger Mergify actions by commenting on this pull request:

• @Mergifyio refresh will re-evaluate the rules
• @Mergifyio rebase will rebase this PR on its base branch
• @Mergifyio update will merge the base branch into this PR
• @Mergifyio backport <destination> will backport this PR on <destination> branch

Additionally, on Mergify dashboard you can:

• look at your merge queues
• generate the Mergify configuration with the config editor.

Finally, you can contact us on https://mergify.com

---

Original PR Body

The best example of why this is useful is the test showing some possible uses with Valid:

object ValidExtensions {
  implicit def view[T <: Data] = DataView[T, Valid[T]](
    x => Valid(x.cloneType), // Valid will strip direction with `Output(...)` anyway
    _ -> _.bits,
    (_, v) => true.B -> v.valid
  )
}

This enables you to box any T as a Valid[T] where the valid bit is the literal true:

import ValidExtensions._
class MyModule extends Module {
  val in = IO(Input(UInt(8.W)))
  val out= IO(Output(Valid(UInt(8.W))))
  out := in.viewAs[Valid[UInt]]
}

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

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 or 3.6.x depending on impact, API modification or big change: 5.0.0)?
• 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.