debug: use the new `[]string` type buildFlags

[hyangah]

Newer versions of delve started to support []string type BuildFlags in the launch config. go-delve/delve#2718.
We need to change our extension to utilize it when delve is new enough to understand it.

We hope that this can help issues like
#1831
#1027

(I think there are more related open issues. I will link them later)

[gopherbot]

Change https://go.dev/cl/538057 mentions this issue: src/goDebugConfiguration: allow buildFlags passed in array