style-guide: add guidelines for standard streams; fix remaining pages (#11196)

* readonly, {un,}compress, zbarcam: use proper syntax for IO streams

* style-guide: add guidelines for standard streams

* duckdb, perl: add backticks around stdin and stdout

contributing-guides/style-guide.md

@@ -180,6 +180,7 @@ Use backticks on the following:
 - Paths, e.g. `package.json`, `/etc/package.json`.
 - Extensions, e.g. `.dll`.
 - Commands, e.g. `ls`.
+- Standard streams: `stdout`, `stdin`, `stderr`. **Do not** use the full names (e.g. standard output).
 
 ## Descriptions