This is a custom extension OSC 117.

Fixes an issue with std not being disabled when building
vte without std feature.

The `no_std` feature has been broken since version `0.14`, since it did
not disable the `std` feature of `memchr`.

To fall more in line with the general ecosystem standards, this crate
changes the `no_std` feature into an `std` feature. Since `vte` should
be significantly faster with this feature, it has also been enabled by
default (previously `no_std` was default).

This is a breaking change, even if we ignore `no_std` consumers which
aren't able to compile 0.14, since intermediate dependencies relying on
the `no_std` feature will have to remove it from the manifest.

See https://vt100.net/docs/vt510-rm/DECST8C.html.

The table based state change was too complex to make guesses why it's
getting slow and too fragile, as in modifying the amount of
states/actions were slowing down, even though, they were not used.

Rewrite the state + action change exactly how it's in [1] with respect
to our modifications/C1, etc. The new implementation is generally faster
than the previous one and is easier for compiler to reason about and
generate more efficient structures.

Also, the structure got way simpler to follow, since it matches the
spec pretty much exactly.

[1] - https://vt100.net/emu/dec_ansi_parser

If the valid character was split across reads of partial utf8 and
got terminated by invalid byte, we should print it and advance, instead
of trying to discard it entirely.