Use the `description` property of `@metadata()` decorator to populate hover detail

**Is your feature request related to a problem? Please describe.**
There are two ways to include a description in the compiled output of a Bicep template: by using the `@description()` decorator or by including a `description` property at the top level of the content of a `@metadata()` decorator. The former will be used as descriptive detail in hovers/tooltips, whereas the latter will not.

**Describe the solution you'd like**
When a description is provided via `@metadata()`, that description should appear in hovers.

The issue does not name files, tests, or an entry point. Start by locating the code that builds hover details and reads @metadata() content, then find existing hover tests. Done means a top-level metadata description appears in the relevant hovers, alongside descriptions supplied through @description().

Written by the indexing model from the issue text.