Except for the indent visitor bits.
Tests for parse_util_detect_errors* are not ported yet because they depend
on expand.h (and operation_context.h which depends on env.h).
Most of it is duplicated, hence untested.
Functions like mbrtowc are not exposed by the libc crate, so declare them
ourselves.
Since we don't know the definition of C macros, add two big hacks to make
this work:
1. Replace MB_LEN_MAX and mbstate_t with values (resp types) that should
be large enough for any implementation.
2. Detect the definition of MB_CUR_MAX in the build script. This requires
more changes for each new libc. We could also use this approach for 1.
Additionally, this commit brings a small behavior change to
read_unquoted_escape(): we cannot decode surrogate code points like \UDE01
into a Rust char, so use � (\UFFFD, replacement character) instead.
Previously, we added such code points to a wcstring; looks like they were
ignored when printed.
