devel/jsonnet: Update 0.20.0 => 0.21.0

Changelog:
https://github.com/google/jsonnet/releases/tag/v0.21.0

• Replace the bundled rapidyaml hpp file with a newer one for compatibility with devel/rapidyaml.
• Refresh patches.
• Replace PORTVERSION with DISTVERSION and VERSION in PLIST_SUB.

PR: 287756
Approved by: Gasol Wu <gasol.wu@gmail.com> (maintainer)
Co-authored-by: Pavel Timofeev <timp87@gmail.com>