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/script-setup.vim

@@ -16,3 +16,4 @@ function! Check()
   call ExpectNoSyntax('value < 3', 'vue3Keyword')
   call ExpectSyntax('defineExpose', 'vue3Keyword')
 endfunction
+let g:test_flatten = 1