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/attribute-off.vue

@@ -0,0 +1,13 @@
+<template>
+  <div @click="toggle(item)" :title="$t('title')" v-if="count > 1">
+    <p>{{ message }}</p>
+  </div>
+</template>
+
+<script>
+export default {
+  data() {
+    return {}
+  },
+}
+</script>