GitHub Action workflows had tool installation commands defined
in .yml file while Kokoro CI used a bash script. This change
made them to share the same logic.

Instead of using the existing build/all.bash script, this CL
reimplemented the installation logic in go

- to have one single program for all platforms (linux, windows, mac)
- to implement complex logic that switches between go get and
go install depending on the go version (versioned binary installation
using go install became available only after 1.16.

Updates golang/vscode-go#1825

Change-Id: I295856e7d2bdd2d1fc07efc1e794eccb42b55ad6
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/359397


Trust: Hyang-Ah Hana Kim <hyangah@gmail.com>
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Suzy Mueller <suzmue@golang.org>