[Feature request] Highlighting within inline templates

# 🚀 feature request

### Description
When the cursor is placed on any tag within an inline template, the entire template is highlighted. In external HTML templates, just the opening and the closing tag are highlighted. I assume this is the case because the language mode of the file is set to TypeScript, not HTML. I find this very annoying.

### Feature Type
What does this bug affect

- [x] Angular Language Service VSCode extension
- [ ] Angular Language Service server

### Describe the solution you'd like
Ideally the language mode of inline templates would be set to HTML.

### Describe alternatives you've considered
Have you considered any alternative solutions or workarounds?
I have tried using other extensions, like [Inline HTML](https://marketplace.visualstudio.com/items?itemName=pushqrdx.inline-html) that should change the language mode of template strings with moderate success.

### Anything else relevant?

How it is:

What I would expect:

Start by reproducing the highlighting behavior in the Angular Language Service VSCode extension with an inline template and an external HTML template. Trace how inline templates receive their language mode, then verify that only the matching opening and closing tags are highlighted and that the full template is no longer selected.

Written by the indexing model from the issue text.