linter should flag unnecessary dependsOn with existing resources

linter should flag a resource that has a manually added dependsOn for an existing resource... during compilation we do the right thing (and don't add the dependency), we should flag the dead code in the editor

```bicep
resource ip 'Microsoft.Network/publicIPAddresses@2022-01-01' existing = {
name: 'foo'
}

resource as 'Microsoft.Compute/availabilitySets@2022-03-01' = {
name: 'bar'
location: location
dependsOn: [ ip ]
}
```

Use the issue's Bicep example as the reproduction case, then locate the linter entry point that analyzes dependsOn and existing resources. Done means the editor reports manually added dependencies on existing resources while compilation continues to avoid adding that dependency.

Written by the indexing model from the issue text.