Most of this is just "remember to specify the inputs and outputs on
the command line, so remote-run can see them". A bit is "prefix
environment variables with '%env-'". And the last few are "yeah,
this was never going to work in a remote environment".
In the few cases where I couldn't think of anything reasonable, I just
marked the test as "UNSUPPORTED: remote_run", a new "feature".
Create a _StringRepresentation struct to standardize internal testing
on. Internalize much of _StringGuts, except for some SPI hacks, and
update tests to use _StringRepresentation.
Non-tagged NSStrings carry identity separate from their
value. Continue to bridge them lazily, even if they could fit in small
form, to respect this and avoid potential information loss.
Temporarily disable invariant that all natives strings that could be
small, are.
