tidy-up: miscellaneous

tidy-up: miscellaneous

- H3 proxy: re-sync code with original source `curl_ngtcp2.c` to reduce
  differences, and to apply missed minor fixes. Also apply clang-format.
  Drop redundant `#undef`s, casts, `#endif` comments, includes, drop
  intermediate variables, sync include and macro order.
  Follow-up to e78b1b3eccfa6a2e367a1225ea1b66dafcdac3c4 #21153
- INSTALL-CMAKE.md: move `CURL_ENABLE_SMB` to the enable section.
- tests/http/env: rename `tcpdmp` to `tcpdump` to match object variable.
- mbedtls: drop incorrect `mbedTLS 4+` comments.
  (features are also supported by 3+, meaning it's always supported.)
- lib1648: rename a variable to match purpose.
- CIPHERS.md: alpha-sort link list.
- replace rare `X''` hex markup with `0x`.
- `IP v4/6` -> `IPv4/6`.
- 'version X.Y' -> 'vX.Y', where sensible.
- 'VX.Y' -> 'vX.Y', where sensible.
- fix indents, casing, newlines, typos.

Closes #21772