Add comments for some extensions + test

indent/graphql.vim

@@ -62,6 +62,13 @@ function GetGraphQLIndent()
     return 0
   endif
 
+  " If the previous line isn't GraphQL, don't change this line's indentation.
+  " Assume we've been manually indented as part of a template string.
+  let l:stack = map(synstack(l:prevlnum, 1), "synIDattr(v:val, 'name')")
+  if get(l:stack, -1) !~# '^graphql'
+    return -1
+  endif
+
   let l:line = getline(v:lnum)
 
   " If this line contains just a closing bracket, find its matching opening