Support vue mustache expressions via defineTemplateBodyVisitor

[bradzacher]

Following on from #760 (comment)

For better interop with vue, we might want to look at implementing defineTemplateBodyVisitor.
https://github.com/mysticatea/vue-eslint-parser/blob/0f241279dc412ff4bb0faa9211233a944465f9b4/README.md#L93-L99

This will let plugins provide linting for vue expressions.

[uniqueiniquity]

FWIW, I'm not sure that this is a parser issue, but rather a plugin issue. From what I can tell, it has to be used in each rule. Would be curious to hear from @mysticatea why it's used instead of the built-in visitorKeys feature.

[mysticatea]

Because to not break the core rules.

Vue.js templates have interpolations, floating JavaScript expressions, then those confuse the core rules seriously. Therefore, we have to separate the template's AST from the script.

[bradzacher]

interesting, that makes sense.

Is this something we should ignore entirely then from our end, or are there some cases we could potentially be supporting from within our plugin?