feat: syntax highlight inline template

[znck]

This PR includes syntax highlight support for inline templates, e.g.: fig. 1.

Fig. 1: Inline template syntax highlight

Any object with a string template key is highlighted, e.g.:

const A = Vue.defineComponent({
    template: '<div />' // or "<div />"
})
const B = Vue.defineComponent({
    template: `<div />`
})

Theming

Adequate class names are added to customize the appearance of different tokens, see fig. 2.

Fig. 2: Token classes to style parts of a directive.

Caveats

1. Cannot highlight in an invalid JavaScript snippet.

   const app = Vue.createApp(...)
   //                        ^^^ invalid

   const app = Vue.createApp(/* ... */)
   //                           ^^^ valid

2. Cannot highlight template strings with interpolation.

   const app = Vue.createApp({
       template: `
           <div attr="${foo}" />
       `//            ^^^^^^ highlight is aborted due to interpolation expression. 
   })

Bonus

You can use this highlighter for template snippets too, just use vue-html as language.

    Example snippet:
    
    ```vue-html
    <div v-bind="$attrs" />
    ```

[NataliaTepluhina]

Thanks Rahul! This looks great

[phanan]

This is wonderful. I'm only adding several super minor CS "fixes," which can pretty much be ignored.