Add (undocumented) option to disable name scopes process wide.
Add (undocumented) option to disable name scopes process wide.

When profiling it can be frustrating to see two "trampoline" methods before user
code (_decorate_unbound_method -> wrap_with_name_scope). This environment
variable disables name scoping (and thus those trampolines) everywhere apart
from `__init__`.

Note that you probably only want to enable this environment variable once you
have ruled out that the overhead (entering and exiting a `tf.name_scope`) from
the trampoline methods is not significant for your problem.

PiperOrigin-RevId: 271959140
Change-Id: I826aa9cb9e8c4a5a6584afff5a6567c456446afb

deepmind/sonnet,deepmind/sonnet