Please describe what the rule should do:

It would be nice to make the core rule no-implicit-coercion work in <template> expressions.

What category should the rule belong to?

[] Enforces code style (layout)
[ ] Warns about a potential error (problem)
[X] Suggests an alternate way of doing something (suggestion)
[ ] Other (please specify:)

Provide 2-3 code examples that this rule should warn about:

<template>
  <div :data-foo="!!foo" />
  <div :data-foo="~foo.indexOf('.')" />
  <div :data-foo="+foo" />
  <div :data-foo="1 * foo" />
  <div :data-foo="'' + foo" />
  <div :data-foo="`` + foo" />
  <!-- if the `disallowTemplateShorthand` option is enabled -->
  <div :data-foo="`${foo}`" />
</template>