Fix issue with token mapping for lint errors on template tokens in gjs/gts files by displaying eslint error on the opening <template> tag

[hmajoros]

Background
when using ESLint with gts/gjs files and encountering a lint error specifically on a template token, the error maps to the private __GLIMMER_TEMPLATE scope syntax, and we need to re-map that back into the template. In previous iterations of trying to map these tokens back to the original source, there were a few issues encountered:

- token mapping was too eager, and would match the first instance of a token (even if it was part of a comment block)

// comment Foo <-- this gets caught
<template> <Foo /> </template> // <-- this doesn't

- token mapping never handled multiple tokens, eg:

<template>
  <Foo />
  <Foo /> {{! this one never gets reported by eslint }}
</template>

What does this PR do?
We decided it would be easier (and less bug-prone) to instead just map any eslint errors on scope tokens back to the opening template tag. These error messages are modified to be prefixed with Error in template: , and will still give the user a signal that something is wrong in their template. This code will also be more efficient than searching the code for specific instances of tokens and filtering out any instances determined to be contained inside of a comment block.

This PR updates the logic to handle reporting on scope tokens. If we get a diagnostic message from eslint which is on a scope token, we search backwards until we find the first <template> tag, then we re-print the error message on this line.

[NullVoxPopuli]

LGTM. let's shippit