Support generics when deriving Parser in scala 3

[eejbyfeldt]

Currently when trying to derive a parser for the new test case fails with

-- Error: alexarchambault/case-app/tests/shared/src/test/scala/caseapp/CaseAppTests.scala:632:42 
632 |        Parser[GenericArgs[SharedOptions]].detailedParse(
    |                                          ^
    |Exception occurred while executing macro expansion.
    |java.lang.Exception: No given caseapp.core.parser.Parser[Shared] instance found
    |	at caseapp.core.parser.LowPriorityParserImplicits$.headParserExpr$lzyINIT1$1(LowPriorityParserImplicits.scala:165)
    |	at caseapp.core.parser.LowPriorityParserImplicits$.headParserExpr$1(LowPriorityParserImplicits.scala:166)
    |	at caseapp.core.parser.LowPriorityParserImplicits$.$anonfun$15(LowPriorityParserImplicits.scala:200)
    |	at caseapp.core.parser.LowPriorityParserImplicits$.$anonfun$adapted$2(LowPriorityParserImplicits.scala:202)
    |	at dotty.tools.dotc.quoted.PickledQuotes$$anon$1.transform(PickledQuotes.scala:110)
    |	at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1544)
    |	at dotty.tools.dotc.quoted.PickledQuotes$$anon$1.transform(PickledQuotes.scala:135)
    |	at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform$$anonfun$1(Trees.scala:1614)
    |	at scala.collection.immutable.List.mapConserve(List.scala:473)
    |	at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1614)
    |	at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1510)
    |	at dotty.tools.dotc.quoted.PickledQuotes$$anon$1.transform(PickledQuotes.scala:135)
    |	at dotty.tools.dotc.quoted.PickledQuotes$.spliceTerms(PickledQuotes.scala:152)
    |	at dotty.tools.dotc.quoted.PickledQuotes$.unpickleTerm(PickledQuotes.scala:88)
    |	at scala.quoted.runtime.impl.QuotesImpl.unpickleExprV2(QuotesImpl.scala:3185)
    |	at caseapp.core.parser.LowPriorityParserImplicits$.$anonfun$6(LowPriorityParserImplicits.scala:202)
    |	at scala.collection.immutable.List.foldRight(List.scala:353)
    |	at caseapp.core.parser.LowPriorityParserImplicits$.tupleParserImpl(LowPriorityParserImplicits.scala:110)
    |	at caseapp.core.parser.LowPriorityParserImplicits$.inline$tupleParserImpl(LowPriorityParserImplicits.scala:77)
    |
    |---------------------------------------------------------------------------
    |Inline stack trace
    |- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    |This location contains code that was inlined from LowPriorityParserImplicits.scala:76
 76 |    ${ tupleParserImpl[T] }
    |    ^^^^^^^^^^^^^^^^^^^^^^^
    |- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    |This location contains code that was inlined from LowPriorityParserImplicits.scala:76
246 |    val parser = LowPriorityParserImplicits.tupleParser[T]
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     ---------------------------------------------------------------------------
one error found

[eejbyfeldt]

Also noticed that default values did not work for case class using generics. So added another commit: 27ff11a fixing that as well.