[SPE-2702] Ergonomics Improvements

[ThomasRooney]

1. Solve https://github.com/hashicorp/terraform-plugin-framework/issues/898 via altering Required: true to instead use NotNull validators when under complex nested attributes (array,object, additionalProperties, oneOf types) that are Computed+Optional. This results in less unexpected plan changes
2. Use ValueStringPointer where possible in the RefreshFrom data mapping methods to reduce code required to do data mapping from strict SDK calls.
3. Fix an issue with complex additionalProperties schema types (map types) that could miss some expected plan changes.
4. There's dead code in the %s_sdk.go data mapping methods to be cleared when under a nested attribute.

_{From SyncLinear.com | SPE-2702}