[XLA:Python] Switch C++ jit dispatch path to use PEP 590 vectorcalls.

vectorcalls were introduced in Python 3.8, and now that we have dropped Python 3.7 there's no downside to using them.

```
name        old cpu/op  new cpu/op  delta
jit_simple  3.28µs ±28%  2.94µs ± 2%  -10.63%  (p=0.027 n=10+8)

name        old time/op             new time/op             delta
jit_simple  3.29µs ±28%             2.94µs ± 2%  -10.62%         (p=0.027 n=10+8)
```

Treat the benchmark with a grain of salt: when benchmarking in the 2-3us regime my workstation VM is a bit noisy.

PiperOrigin-RevId: 493592959

Author: hawkinsp

xla/python/BUILD

@@ -398,6 +398,7 @@ cc_library(
         ":python_utils",
         ":pytree",
         ":types",
+        ":util",
         "@com_google_absl//absl/container:flat_hash_map",
         "@com_google_absl//absl/container:inlined_vector",
         "@com_google_absl//absl/strings",
@@ -549,6 +550,7 @@ cc_library(
         ":py_client",
         ":python_utils",
         ":types",
+        ":util",
         "@com_google_absl//absl/hash",
         "@com_google_absl//absl/strings",
         "@com_google_absl//absl/strings:str_format",