fix rendering of field names with backticks

[fwbrasil]

Problem

I've been using PPrint with case classes that contain text field names using backticks, which are currently rendered incorrectly:

case class Test(`with backticks`: Boolean, withoutBackticks: Boolean)
println(pprint(Test(true, false)).plainText)

Outputs both field names without backticks:

Test(with backticks = true, withoutBackticks = false)

It should print:

Test(`with backticks` = true, withoutBackticks = false)

Solution

Change ProductSupport to add backticks in case the field name isn't a regular identifier.

Notes

• The identifier check is based on the implementation in Scala 3. I believe it hasn't changed from Scala 2.
• The ProductSupport class seems identical in Scala 2 and 3. Should change it to use a single implementation for both?
• I wasn't able to run the build locally. What command should I use? ./mill and sbt compile both fail.