Running a file like:
```
import "@std/dotenv/load";
```
Without a mapping in `imports` field of `deno.json` or `dependencies` of
`package.json`
will now error out with a hint:
```
error: Relative import path "@std/dotenv/load" not prefixed with / or ./ or ../
hint: Try running `deno add @std/dotenv/load`
at [WILDCARD]bare_specifier_without_import/main.ts:1:8
```
Closes https://github.com/denoland/deno/issues/24699
---------
Co-authored-by: David Sherret <dsherret@users.noreply.github.com>
