Parse GDB/MI results directly instead of going via JSON (bug#44173)

Parse GDB/MI results directly instead of going via JSON (bug#44173)

Translating GDB/MI into JSON is an unnecessary and fragile detour
that made it hard to deal with octal escapes in strings correctly.
Parse GDB/MI directly instead.

* lisp/progmodes/gdb-mi.el (gdb-mi-decode-strings): Adjust doc string.
(gdb-mi-decode, gud-gdbmi-marker-filter): Remove gdb-mi-decode.
(gdb-jsonify-buffer): Remove.
(gdb-mi--parse-tuple-or-list, gdb-mi--parse-c-string)
(gdb-mi--parse-value, gdb-mi--parse-result-or-value)
(gdb-mi--parse-results, gdb-mi--fix-key, gdb-mi--extend-fullname)
(gdb-mi--c-string-from-string): New functions.
(gdb-json-read-buffer, gdb-json-string, gdb-json-partial-output):
Rename to gdb-mi--read-buffer, gdb-mi--from-string and
gdb-mi--partial-output respectively.  Remove useless FIX-LIST
argument.  FIX-KEY is now a symbol, not a string. All callers updated.
(gdb-tooltip-print, gdbmi-bnf-log-stream-output, gdb-internals)
(gdb-console, gdb-done-or-error, gdb-get-source-file-list)
(gdb-get-prompt, gdb-get-source-file):
Use gdb-mi--c-string-from-string instead of 'read'.
* test/lisp/progmodes/gdb-mi-tests.el: New file.