package.json: limit file search scope for extension activation

Previously, the extension was configured to be activated if the workspace
contains .go files. This is problematic when the workspace is large and
VS Code couldn't complete file search within 7sec - then VS Code will just
activate the extension and gopls & extension will try to scan the workspace
which makes the problem worse for nothing.

Fixes golang/vscode-go#1894

Change-Id: Iaa3d2759eec7ede76780e1f814958a1bbcd83992
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/366916
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: Robert Findley <rfindley@google.com>
diff --git a/package.json b/package.json
index 5ba4d75..eabc1c2 100644
--- a/package.json
+++ b/package.json
@@ -91,8 +91,10 @@
     "vscode": "^1.59.0"
   },
   "activationEvents": [
-    "workspaceContains:**/*.go",
     "onLanguage:go",
+    "workspaceContains:*.go",
+    "workspaceContains:*/*.go",
+    "workspaceContains:*/*/*.go",
     "onCommand:go.gopath",
     "onCommand:go.tools.install",
     "onCommand:go.locate.tools",