CI: add whitespace checker

Fix issues detected.

Also:

- One of the `.vc` files used LF EOLs, while the other didn't.
  Make that one also use LF EOLs, as this is apparently supported by
  `nmake`.

- Drop `.dsw` and `.btn` types from `.gitattributes`.
  The repository doesn't use them.

- Sync section order with the rest of files in
  `tests/certs/EdelCurlRoot-ca.prm`.

- Indent/align `.prm` and `.pem` files.

- Delete dummy `[something]` section from `.prm` and `.pem` files.

Mental note:
MSVC `.sln` files seem to accept spaces for indentation and also support
LF line-endings. I cannot test this and I don't know what's more
convenient when updating them, so left them as-is, with specific
exclusions.

Closes #14031

docs/HTTP3.md

@@ -235,7 +235,7 @@ Build curl:
      % git clone https://github.com/curl/curl
      % cd curl
      % autoreconf -fi
-     % LDFLAGS="-Wl,-rpath,<somewhere>/lib" ./configure --with-openssl=<somewhere> --with-openssl-quic --with-nghttp3=<somewhere2> 
+     % LDFLAGS="-Wl,-rpath,<somewhere>/lib" ./configure --with-openssl=<somewhere> --with-openssl-quic --with-nghttp3=<somewhere2>
      % make
      % make install