Apply our (very) basic syntax highlighting to .vim files (not just .vimrc)

Also change contributed language's name to "Vimscript", which I don't think should break anything

package.json

@@ -1154,8 +1154,9 @@
     },
     "languages": [
       {
-        "id": "vimrc",
+        "id": "Vimscript",
         "extensions": [
+          ".vim",
           ".vimrc"
         ],
         "configuration": "./language-configuration.json"
@@ -1163,9 +1164,9 @@
     ],
     "grammars": [
       {
-        "language": "vimrc",
-        "scopeName": "source.vimrc",
-        "path": "./syntaxes/vimrc.tmLanguage.json"
+        "language": "Vimscript",
+        "scopeName": "source.vimscript",
+        "path": "./syntaxes/vimscript.tmLanguage.json"
       }
     ]
   },

syntaxes/vimscript.tmLanguage.json

@@ -1,8 +1,8 @@
 {
   "$schema": "https://raw.githubusercontent.com/martinring/tmlanguage/master/tmlanguage.json",
-  "name": "vimrc",
-  "fileTypes": [".vimrc"],
-  "scopeName": "source.vimrc",
+  "name": "Vimscript",
+  "fileTypes": [".vim", ".vimrc"],
+  "scopeName": "source.vimscript",
   "patterns": [
     {
       "name": "comment.line",