Add .vscode/ to .gitignore template (#13697)

Adds .vscode/ to the .gitignore rules generated on flutter create.

packages/flutter_tools/templates/create/.gitignore.tmpl

diff --git a/packages/flutter_tools/templates/create/.gitignore.tmpl b/packages/flutter_tools/templates/create/.gitignore.tmpl
index eb15c3d..3b9b8ba 100644
--- a/packages/flutter_tools/templates/create/.gitignore.tmpl
+++ b/packages/flutter_tools/templates/create/.gitignore.tmpl
@@ -1,6 +1,7 @@
 .DS_Store
 .atom/
 .idea
+.vscode/
 .packages
 .pub/
 build/