DISC: Directory for code "upstream" from _libs
Motivated in part by #24737, which is discussing vendoring `tzlocal` for use in `tslibs`.

A lot of effort has gone into making `_libs`, and in particular `tslibs`, self-contained within the pandas code base.  This makes these parts of the code base much easier to reason about.  It also makes it easier to test, profile, and measure coverage on pieces of the code base in isolation.

Furthermore, outside of `_libs` the dependency structure is not quite DAG, but bears a resemblance if you squint and tilt your head a little: `compat`, `errors`, and `util._*` are _almost_ independent of `core`.  `core.dtypes` is almost-independent of the rest of core, etc.

AFAICT there are two pieces of code that prevent us from further simplifying the dependency structure: `config.get_option` and `pprint_thing`.

The proposal is to put these two functions in a directory that is explicitly "upstream" of everything else, allowing us to simplify the dependency structure.

[Side-note: It might also make sense to make a `config` shared within the ecosystem to de-duplicate e.g. `pd.set_option('display.width', ...)` and `np.set_printoption(...)`]

Thoughts?