tidy-up: miscellaneous

- examples: sync debug output printf masks.
- INSTALL-CMAKE.md: tidy up section for some options.
- curl_sha512_256: delete comment suggesting an optimization.
- vtls/keylog: scope a variable.
- vtls/openssl: make a source code URL a permalink.
- vtls/schannel: drop redundant parentheses.
- test1119.pl: robustify `$1` -> `$s`.
- sync arg names in comments to match the code.
- tidy up and minor fixes to comments.
- fix formatting/indenting/comment/newline/include nits.
- move `UNITTEST` protos next to definitions, sync their argument names.
- make variables static.
- add parentheses to Perl `open()` calls.
- drop unnecessary double quotes in Perl.
- clang-format.

Closes #21000

.github/workflows/http3-linux.yml

@@ -427,7 +427,8 @@ jobs:
           - name: 'openssl4'
             install_steps: skipall
             LDFLAGS: -Wl,-rpath,/home/runner/openssl4/build/lib
-            PKG_CONFIG_PATH: "/home/runner/openssl4/build/lib/pkgconfig:\
+            PKG_CONFIG_PATH: "\
+              /home/runner/openssl4/build/lib/pkgconfig:\
               /home/runner/nghttp3/build/lib/pkgconfig:\
               /home/runner/nghttp2-openssl4/build/lib/pkgconfig"
             configure: >-
@@ -435,7 +436,8 @@ jobs:
 
           - name: 'openssl4'
             tflags: '--min=1640'
-            PKG_CONFIG_PATH: "/home/runner/openssl4/build/lib/pkgconfig:\
+            PKG_CONFIG_PATH: "\
+              /home/runner/openssl4/build/lib/pkgconfig:\
               /home/runner/nghttp3/build/lib/pkgconfig:\
               /home/runner/ngtcp2-openssl4/build/lib/pkgconfig:\
               /home/runner/nghttp2/build/lib/pkgconfig"
@@ -483,7 +485,8 @@ jobs:
 
           - name: 'boringssl'
             tflags: '--min=1790'
-            PKG_CONFIG_PATH: "/home/runner/boringssl/build/lib/pkgconfig:\
+            PKG_CONFIG_PATH: "\
+              /home/runner/boringssl/build/lib/pkgconfig:\
               /home/runner/nghttp3/build/lib/pkgconfig:\
               /home/runner/ngtcp2-boringssl/build/lib/pkgconfig:\
               /home/runner/nghttp2/build/lib/pkgconfig"
@@ -503,7 +506,8 @@ jobs:
             install_packages: libp11-kit-dev libssh-dev
             tflags: '--min=1840'
             LDFLAGS: -Wl,-rpath,/home/runner/gnutls/build/lib
-            PKG_CONFIG_PATH: "/home/runner/nettle/build/lib64/pkgconfig:\
+            PKG_CONFIG_PATH: "\
+              /home/runner/nettle/build/lib64/pkgconfig:\
               /home/runner/gnutls/build/lib/pkgconfig:\
               /home/runner/nghttp3/build/lib/pkgconfig:\
               /home/runner/ngtcp2/build/lib/pkgconfig:\