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.vim

@@ -0,0 +1,14 @@
+" Without attribute and keyword highlight
+let g:vim_vue_plugin_config = {'attribute': 0, 'keyword': 0}
+let g:test_flatten = 1
+
+function! Check()
+  call ExpectSyntax('@click', 'VueKey')
+  call ExpectSyntax('toggle', 'VueValue')
+  call ExpectNoSyntax('$t', 'VueInject')
+  call ExpectNoSyntax('1"', 'javaScriptNumber')
+  call ExpectSyntax('message', 'VueExpression')
+  call ExpectEqual(matchstr(execute('highlight VueKey'), 'links to \zs\S\+'),
+        \ 'htmlArg', 'VueKey link')
+  call ExpectNoSyntax('data', 'vueObjectFuncName')
+endfunction