Optimize BitPat factory from UInt literals (backport #3988)

[mergify]

Benchmarked using #3987,

For BitPat(0xdeadbeefL.U) 72x speedup:

Benchmark                           Mode  Cnt   Score   Error   Units
ChiselBenchmark.BitPatFromUInt     thrpt   10  42.105 ± 1.364  ops/us
ChiselBenchmark.BitPatFromUIntOld  thrpt   10   0.582 ± 0.005  ops/us

For BitPat(3.U) 7x speedup:

Benchmark                           Mode  Cnt   Score   Error   Units
ChiselBenchmark.BitPatFromUInt     thrpt    3  44.501 ± 7.054  ops/us
ChiselBenchmark.BitPatFromUIntOld  thrpt   10   5.819 ± 0.049  ops/us

For real design, reduced amount of time in BitPat.apply from 116 seconds to 12.5 seconds (9x speedup)

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

• Performance improvement

Desired Merge Strategy

• Squash

Release Notes

Speeds up conversion of UInt literals to BitPat by ~9x in practice, ~70x for large UInts.

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: 3.6.x, 5.x, or 6.x depending on impact, API modification or big change: 7.0)?
• 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.

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This is an automatic backport of pull request #3988 done by [Mergify](https://mergify.com).