[TASK] Remove deprecated/unnecessary rolling-window overloads

Given that the rolling-window (and grouped rolling window) functionality is roughly stable, it would make sense to remove any unnecessary overloads that were introduced during development.

Examples:

1. `grouped_time_range_rolling_window()` was generalized to `grouped_range_rolling_window()`, which also happens to work with time ranges. The former can be removed.
2. The older `rolling_window()` and `grouped_rolling_window()` methods took `preceding`/`following` bounds as `size_type`. The `bounds` concept was generalized to a `window_bounds` class, to incorporate `UNBOUNDED PRECEDING`/`UNBOUNDED FOLLOWING`. The older methods can be deprecated in favour of the newer ones.
3. Certain window functions (E.g. `LEAD`/`LAG`) allow for default values. Instead of a separate function with the extra parameter, we should consolidate to a single function with an optional parameter.