internal/goexperiment: add aliastypeparams GOEXPERIMENT flag

For #46477.

Change-Id: Ic917272cb2cd28dcb39f173b3cdcfb72e52eae2d
Reviewed-on: https://go-review.googlesource.com/c/go/+/586955
Reviewed-by: Robert Griesemer <[email protected]>
Reviewed-by: Austin Clements <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Robert Griesemer <[email protected]>

Author: griesemer

src/internal/goexperiment/exp_aliastypeparams_off.go

@@ -110,4 +110,9 @@ type Flags struct {
 
 	// RangeFunc enables range over func.
 	RangeFunc bool
+
+	// AliasTypeParams enables type parameters for alias types.
+	// Requires that gotypesalias=1 is set with GODEBUG.
+	// This flag will be removed with Go 1.24.
+	AliasTypeParams bool
 }