gopls: report file change notifications for "gopls.mod"

[stamblerre]

Right now, we only look at files with the name go.mod, but for multi-module workspace support, we also need file change notifications for the gopls.mod "configuration" file.

[hyangah]

I think these are the relevant code path:

vscode-go/src/goLanguageServer.ts

Line 223 in 9bf9d64

documentSelector: ['go', 'go.mod', 'go.sum'],

vscode-go/package.json

Lines 110 to 118 in 9bf9d64

	"id": "go.mod",
	"extensions": [
	"go.mod"
	],
	"aliases": [
	"Go Module File"
	],
	"configuration": "./languages/go.mod.language-configuration.json"
	},

(not sure why go.mod is configured in the extension property...)

[gopherbot]

Change https://golang.org/cl/263986 mentions this issue: package.json: recognize gopls.mod as a go.mod file

[hyangah]

while testing cl/263986, I noticed that gopls already receives workspace/didChangeWatchedFiles on gopls.mod files.
cl/263986 makes features like code lenses, diagnostics, etc become available to gopls.mod files. Given the limited purpose of gopls.mod, I am not yet sure if this is necessary, or just workspace/didChangeWatchedFiles is sufficient for gopls. @stamblerre

[stamblerre]

We do think that the workspace/didChangeWatchedFiles should be enough for our current purposes, but it might be worth adding this support earlier rather than later in case we need overlays for the gopls.mod for whatever reason.