*/*: Introduce versioned Go ports
- Mk/Uses/go.mk: add support for selecting Go port version in USES=go;
- Mk/bsd.default-versions.mk: add GO_DEFAULT;
- convert lang/go-devel to the master and lang/go{117,118} to slave ports;
- add lang/go meta-port that provides go and gofmt symlinks to the current default version.
PR: 264336
Reviewed by: ygy jwb yuri mikael drtr0jan@yandex.ru decke mat
Differential Revision: https://reviews.freebsd.org/D35346