Remove `ScriptSettingsManager`

As part of the the .NET Core migration, we've updated `ScriptSettingsManager` to use the `IConfiguration` instance that is provided by the host (or build a default one).

This is a temporary solution to avoid having to change every piece of code relying on `ScriptSettingsManager` as part of the migration (which, to be done cleanly, also depends on the hosting work we intend to do).

Creating this to track the work of removing this time in favor of using the configuration provided by the host/DI.

Start by tracing all code that relies on ScriptSettingsManager and compare those paths with the IConfiguration instance supplied by the host or through DI. Review the intended hosting work before changing callers. Done means ScriptSettingsManager is removed and configuration access consistently uses the host-provided configuration without the temporary compatibility layer.

Written by the indexing model from the issue text.