Test all features

Add cases for attribute highlight on and off, block syntax by lang
and emmet-vim group names, OnChangeVueSyntax(), matchit, .wpy,
initial_indent as syntax and tag.syntax, and syntax after reloading.

Also check indenting a file after removing all indent with
g:test_flatten, which fails before the end tag fix as closing tags at
column 0 were taken as block end tags.

test/cases/initial-indent.vue

@@ -0,0 +1,28 @@
+<script>
+export default {}
+</script>
+
+<style lang="scss">
+  .a {
+    color: red;
+  }
+</style>
+
+<style>
+.b {
+  color: blue;
+}
+</style>
+
+<i18n>
+  {
+    "en": {
+      "hello": "Hello"
+    }
+  }
+</i18n>
+
+<i18n lang="yaml">
+en:
+  hello: Hello
+</i18n>