[dev.typeparams] all: merge dev.regabi into dev.typeparams

The files below had conflicts that required manual resolution.
The unresolved conflict in noder.go was just in the import
declaration (trivial). All the other conflicts are in tests
where the ERROR regex patterns changed to accomodate gccgo
error messages (incoming from dev.regabi), and to accomodate
types2 in dev.typeparams. They were resolved by accepting the
dev.regabi changes (so as not to lose them) and then by re-
applying whatever changes needed to make them pass with types2.
Finally, the new test mainsig.go was excluded from run.go when
using types2 due to issue #43308.

	src/cmd/compile/internal/gc/noder.go
	test/fixedbugs/bug13343.go
	test/fixedbugs/bug462.go
	test/fixedbugs/issue10975.go
	test/fixedbugs/issue11326.go
	test/fixedbugs/issue11361.go
	test/fixedbugs/issue11371.go
	test/fixedbugs/issue11674.go
	test/fixedbugs/issue13365.go
	test/fixedbugs/issue13471.go
	test/fixedbugs/issue14136.go
	test/fixedbugs/issue14321.go
	test/fixedbugs/issue14729.go
	test/fixedbugs/issue15898.go
	test/fixedbugs/issue16439.go
	test/fixedbugs/issue17588.go
	test/fixedbugs/issue19323.go
	test/fixedbugs/issue19482.go
	test/fixedbugs/issue19880.go
	test/fixedbugs/issue20185.go
	test/fixedbugs/issue20227.go
	test/fixedbugs/issue20415.go
	test/fixedbugs/issue20749.go
	test/fixedbugs/issue22794.go
	test/fixedbugs/issue22822.go
	test/fixedbugs/issue22921.go
	test/fixedbugs/issue23823.go
	test/fixedbugs/issue25727.go
	test/fixedbugs/issue26616.go
	test/fixedbugs/issue28079c.go
	test/fixedbugs/issue28450.go
	test/fixedbugs/issue30085.go
	test/fixedbugs/issue30087.go
	test/fixedbugs/issue35291.go
	test/fixedbugs/issue38745.go
	test/fixedbugs/issue41247.go
	test/fixedbugs/issue41440.go
	test/fixedbugs/issue41500.go
	test/fixedbugs/issue4215.go
	test/fixedbugs/issue6402.go
	test/fixedbugs/issue6772.go
	test/fixedbugs/issue7129.go
	test/fixedbugs/issue7150.go
	test/fixedbugs/issue7153.go
	test/fixedbugs/issue7310.go
	test/fixedbugs/issue8183.go
	test/fixedbugs/issue8385.go
	test/fixedbugs/issue8438.go
	test/fixedbugs/issue8440.go
	test/fixedbugs/issue8507.go
	test/fixedbugs/issue9370.go
	test/fixedbugs/issue9521.go

Change-Id: I26e6e326fde6e3fca5400711a253834d710ab7f4