Allow lang without quotes and lang="typescript"

<script lang=ts> and <style lang=sass> without quotes weren't
recognized, so they used the first syntax in the config. For sass, it
also flattened the nesting when indenting. lang="typescript" wasn't
recognized either.

Languages not in the config still use the first syntax as before.

test/cases/lang-attr.vim

@@ -0,0 +1,17 @@
+" lang in double or single quotes or without quotes, and
+" lang="typescript"
+let g:vim_vue_plugin_config = {
+      \'syntax': {
+      \   'template': ['html'],
+      \   'script': ['javascript', 'typescript'],
+      \   'style': ['css', 'scss', 'sass'],
+      \},
+      \}
+
+function! Check()
+  call ExpectEqual(GetVueSyntax(), 'html', 'syntax at line 1')
+  call ExpectBlock('let a', 'script', 'typescript', 'typescriptScriptBlock')
+  call ExpectBlock('let b', 'script', 'typescript', 'typescriptScriptBlock')
+  call ExpectBlock('$c', 'style', 'scss', 'cssScssStyleBlock')
+  call ExpectBlock('color: red', 'style', 'sass', 'sassStyleBlock')
+endfunction

test/cases/lang-attr.vue

@@ -0,0 +1,20 @@
+<template lang=html>
+  <div>x</div>
+</template>
+
+<script lang=ts>
+let a: number = 1
+</script>
+
+<script lang="typescript">
+let b: number = 2
+</script>
+
+<style lang='scss'>
+$c: 1px;
+</style>
+
+<style lang=sass>
+p
+  color: red
+</style>