Unify names and build scripts for libs and for wlr-*

[assambar]

• all external libs now use libs/${LIBNAME{/v${VERSION} folder. tag is already set in wlr-env-repo.sh
• all internal libs only use libs/${LIBNAME}
• add separate GH reusable release flow and Makefile macros for external and internal libs targets
• GH reusable workflows are simplified and package *.tar.gz, so build params are reduced
• added README.md for libs/ and a basic one for each lib
• renamed all wasmlabs references to wlr in variables, text and script names
• split the logic in wlr-env.sh into several functions which get called one by one - to make it more readable
• exposed a few more relevant WLR_* variables when running build in a container (with make)

[ereslibre]

Besides @gzurl comments, LGTM. Thanks @assambar! Thanks for the wlr-test scripts, now we are a step closer to piping them to our GH actions!

[gzurl]

Great job! Ship it!