GHA/checksrc: expand spellcheck, fix issues found

- codespell: break logic out into its own runnable script. Allowing
  to run it on local machines.
- codespell: install via `pip`, bump to latest version.
- codespell: show version number in CI log.
- codespell: drop no longer needed word exception: `msdos`.
- codespell: include all curl source tree, except `packages` and
  `winbuild`. Drop an obsolete file exclusion.
- add new spellchecker job using the `typos` tool. It includes
  the codespell dictionary and a couple more. Use linuxbrew to install
  it. This takes 10 seconds, while installing via `cargo` from source
  would take over a minute.
- codespell: introduce an inline ignore filter compatible with `cspell`
  Make `typos` recognize it, too. Move single exceptions inline.

Fix new typos found. Also rename variables and words to keep
spellchecking exceptions at minumum. This involves touching some tests.
Also switch base64 strings to `%b64[]` to avoid false positives.

Ref: https://github.com/crate-ci/typos/blob/master/docs/reference.md
Ref: https://github.com/codespell-project/codespell?tab=readme-ov-file#inline-ignore
Ref: https://github.com/codespell-project/codespell/issues/1212#issuecomment-1721152455
Ref: https://cspell.org/docs/Configuration/document-settings

Closes #17905

docs/libcurl/libcurl.m4

@@ -41,8 +41,8 @@
 # values.  Other useful defines are LIBCURL_FEATURE_xxx where xxx are
 # the various features supported by libcurl, and LIBCURL_PROTOCOL_yyy
 # where yyy are the various protocols supported by libcurl.  Both xxx
-# and yyy are capitalized.  See the list of AH_TEMPLATEs at the top of
-# the macro for the complete list of possible defines.  Shell
+# and yyy are capitalized.  See the list of AH_TEMPLATE macros at the top
+# of the macro for the complete list of possible defines.  Shell
 # variables $libcurl_feature_xxx and $libcurl_protocol_yyy are also
 # defined to 'yes' for those features and protocols that were found.
 # Note that xxx and yyy keep the same capitalization as in the