stdscript: Add v0 treasury gen p2sh benchmark.

BenchmarkIsTreasuryGenScriptHashScript
--------------------------------------
v0_complex_non_standard       814816624   1.310 ns/op   0 allocs/op
v0_treasury_generation_p2sh   520297904   2.274 ns/op   0 allocs/op

This is part of a series of commits to fully implement the stdscript
package.

internal/staging/stdscript/script_bench_test.go

@@ -291,3 +291,13 @@ func BenchmarkIsTreasuryGenPubKeyHashScript(b *testing.B) {
 	}
 	benchIsX(b, filterFn, IsTreasuryGenPubKeyHashScript)
 }
+
+// BenchmarkIsTreasuryGenScriptHashScript benchmarks the performance of
+// analyzing various public key scripts to determine if they are treasury
+// generation p2sh scripts.
+func BenchmarkIsTreasuryGenScriptHashScript(b *testing.B) {
+	filterFn := func(test scriptTest) bool {
+		return test.wantType == STTreasuryGenScriptHash
+	}
+	benchIsX(b, filterFn, IsTreasuryGenScriptHashScript)
+}