src/goVulncheck: copy codicon resources to media

We do not package node_modules in our extension.
Copy the codicon resources to media.
We need to automate the copying process.

Fixes #2455
For #2456

Change-Id: I273fa54d92c42363e7a4bfbe6e7df3f4bd56fb40
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/430715
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
Reviewed-by: Jamal Carvalho <jamal@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>

Author: hyangah