chore: migrate away from GNU-style field designators

[dijkstracula]

This is not a correctness issue, but building semgrep-core currently results in a whole bunch of -Wgnu-designator warnings:

...
bindings.c:64:3: warning: use of GNU old-style field designator extension [-Wgnu-designator]
   64 |   identifier : "TSNode handling",
      |   ^~~~~~~~~~~~
      |   .identifier =
bindings.c:65:3: warning: use of GNU old-style field designator extension [-Wgnu-designator]
   65 |   finalize : custom_finalize_default,
      |   ^~~~~~~~~~
      |   .finalize =
bindings.c:66:3: warning: use of GNU old-style field designator extension [-Wgnu-designator]
   66 |   compare : custom_compare_default,
      |   ^~~~~~~~~
      |   .compare =
bindings.c:67:3: warning: use of GNU old-style field designator extension [-Wgnu-designator]
   67 |   hash : custom_hash_default,
      |   ^~~~~~
      |   .hash =
bindings.c:68:3: warning: use of GNU old-style field designator extension [-Wgnu-designator]
   68 |   serialize : custom_serialize_default,
      |   ^~~~~~~~~~~
      |   .serialize =
bindings.c:69:3: warning: use of GNU old-style field designator extension [-Wgnu-designator]
   69 |   deserialize : custom_deserialize_default
      |   ^~~~~~~~~~~~~
      |   .deserialize =
...

This patch adjusts our binding struct declarations so that do not use the old style designator convention, which squelches the warnings.

Security

• Change has no security implications (otherwise, ping the security team)