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.vim

@@ -0,0 +1,26 @@
+" Template syntax with attribute highlight
+let g:vim_vue_plugin_config = {'attribute': 1}
+let g:test_flatten = 1
+
+function! Check()
+  " Directives
+  call ExpectSyntax(':class', 'VueKey')
+  call ExpectSyntax('@click', 'VueKey')
+  call ExpectSyntax('v-if', 'VueKey')
+  " Values as expressions
+  call ExpectSyntax('1"', 'javaScriptNumber')
+  call ExpectSyntax('$t', 'VueInject')
+  call ExpectSyntax("'title'", 'javaScriptStringS')
+  " Components and attributes
+  normal! gg
+  call ExpectSyntax('MyComponent', 'VueComponentName')
+  call ExpectSyntax('ref=', 'htmlArg')
+  call ExpectSyntax('data-id', 'htmlArg')
+  call ExpectSyntax('my-component', 'VueComponentName')
+  call ExpectSyntax('transition', 'VueComponentName')
+  " Interpolation
+  call ExpectSyntax('{{', 'VueBrace')
+  call ExpectSyntax('message', 'VueExpression')
+  call ExpectEqual(matchstr(execute('highlight VueKey'), 'links to \zs\S\+'),
+        \ 'Type', 'VueKey link')
+endfunction