Resource list* function completions do not have documentation

Screenshot:

Repro (cursor to request completions at marked with `|`):
```bicep
resource stg 'Microsoft.Storage/storageAccounts@2021-09-01' existing = {
name: 'foo'
}

var stgKeys = stg.li|
```

Reproduce the completion request at `stg.li|` in the Bicep example and inspect the resource-list function completion entry. Trace the completion-generation entry point for member functions and add documentation to these entries; done when the completion UI shows documentation for the applicable resource list functions.

Written by the indexing model from the issue text.