[3.5.x] Deprecate named arguments for methods moving to macros in 3.6

[jackkoenig]

These methods will start using def macros and since def macros do not
supported named arguments this will be a source-incompatible change.
This deprecation will warn users that they need to remove any uses of
named arguments on these methods.

This resolves the issue discussed in #2515.

This doesn't give perfect error messages, but it's not bad. For the following

RegEnable(next = 0.U, enable = true.B)

You'll get the warnings:

[warn] .../Example.scala:5:18: naming parameter next is deprecated (since Chisel 3.5).
[warn]   RegEnable(next = 0.U, enable = true.B)
[warn]                  ^
[warn] .../Example.scala:5:32: naming parameter enable is deprecated (since Chisel 3.5).
[warn]   RegEnable(next = 0.U, enable = true.B)
[warn]                                ^

Note as precise as one would like but it does suggest that you should stop using the names 🤷‍♂️

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 state the API impact?
• Did you specify the code generation impact?
• Did you request a desired merge strategy?
• Did you add text to be included in the Release Notes for this change?

Type of Improvement

• code cleanup

API Impact

Warn about impending API change in 3.6.

Backend Code Generation Impact

No impact

Desired Merge Strategy

• Squash

Release Notes

In Chisel 3.6, several chisel3 utils will start using def macros which do not allow named arguments. These utils are: Cat, Fill, FillInterleaved, PopCount, Reverse, RegEnable, ShiftRegister, and ShiftRegisters.

Reviewer Checklist (only modified by reviewer)

• Did you add the appropriate labels?
• Did you mark the proper milestone (Bug fix: 3.4.x, [small] API extension: 3.5.x, API modification or big change: 3.6.0)?
• Did you review?
• Did you check whether all relevant Contributor checkboxes have been checked?
• Did you mark as Please Merge?