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/random.vim

@@ -8,3 +8,4 @@ let g:vim_vue_plugin_config = {
       \'keyword': 1,
       \'foldexpr': 1,
       \}
+let g:test_flatten = 1