debug: require a dev version of delve when operating in Delve DAP mode

[hyangah]

Delve DAP is under active development. Many new features and bug fixes the Delve DAP adapter
depends on will be most likely not available with the stable version of Delve.

Pin required versions with extension release, and ask for update when Delve DAP adapter is used
and the current delve version is older than the required version.

@suzmue @polinasok

Related: #487

[polinasok]

According to @aarzilli, delve "makes one release roughly every 6 months around the time when Go rc1 comes out." Middway releases happen, but are not guaranteed. So to be able to pick up new changes for the new experimental adapter quickly, we definitely need to pin to more recent dev versions, i.e. picking specific commits we like.

[polinasok]

Another thought. Since users might be switching between stable and experimental adapters, we should be careful not to wipe out stable delve to be used with the stable adapter with some recent experimental commit. There should be two separate delve binaries.

[gopherbot]

Change https://golang.org/cl/297189 mentions this issue: src/goInstallTools: install dlv-dap (dev version of dlv)

[gopherbot]

Change https://golang.org/cl/297190 mentions this issue: build,.github/workflows: install dlv-dap

[hyangah]

@suzmue found an issue with the first installation and is preparing a fix for this in https://go-review.googlesource.com/c/vscode-go/+/303235