Backport of "gst-env: Improve documentation" into 1.20
Backport of !1743 (merged) "gst-env: Improve documentation".
Commits:
- cfea4280 gst-env: Improve coding style and cleanup
- 0a65c87e Add documentation for GST_VALIDATE_PLUGIN_PATH
- 278f4a64 Improve environment variable documentation
- 7702072a Add documentation for GST_VALIDATE_APPS_DIR
- c999d2c3 Maintain build instructions at a single location
- 0c8ff1a8 Revert "Allow running gst-uninstalled when gst-build is a subproject"
- 683d0456 tests: Remove deleted gst-env option from test
- 57158f41 Allow running gst-uninstalled when GStreamer is a subproject
- 0b6bbce0 Remove the uninstalled term
- 5a421886 docs: Extend documentation for the GStreamer development environment
- 7063aa14 docs: Fix typos in documentation
- d97e480d meson: Adjust ninja usage restriction info for devenv