replace testdata/scripts/*.txt with testdata/script/*.txtar

Following the best practices from upstream.
In particular, the "txt" extension is somewhat ambiguous.

This may cause some conflicts due to the git diff noise,
but hopefully we won't ever do this again.

testdata/script/typeparams.txtar

@@ -0,0 +1,55 @@
+env GOGARBLE=*
+
+garble build
+! binsubstr main$exe ${WORK} 'garble_main.go' 'GenericFunc' 'GenericVector' 'PredeclaredSignedInteger' 'StringableSignedInteger' 'CombineEmbeds' 'GenericParam'
+
+-- go.mod --
+module test/main
+
+go 1.18
+
+-- garble_main.go --
+package main
+
+func main() {
+	GenericFunc[int, int](1, 2)
+	var _ GenericVector[int]
+
+	g1 := GenericGraph[string]{Content: "Foo"}
+	g1.Edges = make([]GenericGraph[string], 1)
+
+	g2 := GenericGraph[*[]byte]{Content: new([]byte)}
+	g2.Edges = make([]GenericGraph[*[]byte], 1)
+}
+
+func GenericFunc[GenericParamA, B any](x GenericParamA, y B) {}
+
+type GenericVector[GenericParamT any] []GenericParamT
+
+type GenericGraph[T any] struct {
+	Content T
+	Edges []GenericGraph[T]
+}
+
+type PredeclaredSignedInteger interface {
+	int | int8 | int16 | int32 | int64
+}
+
+type StringableSignedInteger interface {
+	~int | ~int8 | ~int16 | ~int32 | ~int64
+
+	String() string
+}
+
+type CombineEmbeds interface {
+	string | int
+
+	interface { EmbeddedMethod() }
+	RegularMethod()
+}
+
+type Slice[T any] []T
+
+func sliceOfPointer() Slice[*any] {
+	return []*any{}
+}