Currently
```
import jax
```
populates `jax._src` in the names exported from JAX. This change prepares for not exporting `jax._src` by default.
In particular, explicitly import modules from jax._src and refer to those imports rather than assuming jax._src contents will be around later. This is a common pattern in tests.
This change does not yet remove any exported names.
Issue https://github.com/google/jax/issues/11951
PiperOrigin-RevId: 469480816
Almost all XLA translation rules have MHLO equivalents at this point, and there are no code paths that use the XLA translation rules in preference to their MLIR equivalents.
PiperOrigin-RevId: 442547482
The main motivation here is ensuring that FFTs are always marked in
profiler results, which is not necessarily the case where running on
TPUs.
I would jit decorate the user facing functions in jax.numpy.fft, but
these functions also accept parameters as lists, e.g., for axes, which
are mutable and hence not valid as direct input into jit decorated
functions. This might be worth doing, but would be a breaking change.
PocketFFT is the same FFT library used by NumPy (although we are using the C++ variant rather than the C variant.)
For the benchmark in #2952 on my workstation:
Before:
```
907.3490574884647
max: 4.362646594533903e-08
mean: 6.237288307614869e-09
min: 0.0
numpy fft execution time [ms]: 37.088446617126465
jax fft execution time [ms]: 74.93342399597168
```
After:
```
907.3490574884647
max: 1.9057386696477137e-12
mean: 3.9326737908882566e-13
min: 0.0
numpy fft execution time [ms]: 37.756404876708984
jax fft execution time [ms]: 28.128278255462646
```
Fixes https://github.com/google/jax/issues/2952
PiperOrigin-RevId: 338743753
