testdata: add generic alias identity regressions

Add cases where same-named local aliases instantiate generic functions,
local types, and methods with float32 and float64. Record the current
collisions and incorrect results.

compiler/testdata/generics.go

@@ -19,12 +19,49 @@ func Add[T Coord](a, b Point[T]) Point[T] {
 	}
 }
 
+func aliasSize[F float32 | float64]() uintptr {
+	return unsafe.Sizeof(F(0))
+}
+
+func aliasSize32() uintptr {
+	type F = float32
+	return aliasSize[F]()
+}
+
+func aliasSize64() uintptr {
+	type F = float64
+	return aliasSize[F]()
+}
+
+type aliasMethodResult[F float32 | float64] struct {
+	Value F
+}
+
+type aliasMethodValue[F float32 | float64] struct{}
+
+func (aliasMethodValue[F]) Get() aliasMethodResult[F] {
+	return aliasMethodResult[F]{}
+}
+
 func main() {
 	var af, bf Point[float32]
 	Add(af, bf)
 
 	var ai, bi Point[int]
 	Add(ai, bi)
+
+	checkSize(aliasSize32())
+	checkSize(aliasSize64())
 }
 
 func checkSize(uintptr)
+
+func checkBool(bool)
+
+func aliasMethod32(x any) {
+	type F = float32
+	_, ok := x.(interface {
+		Get() aliasMethodResult[F]
+	})
+	checkBool(ok)
+}