Further API streamlining for v2

[gboeing]

The development work for v2 has made streamlining the package's API a point of emphasis (see #1106). I propose a couple more streamlining changes to take effect in v2 but have FutureWarnings in v1. The short story is we should deprecate then remove the speed and utils_graph modules by moving their functionality into more sensible modules.

v1.7.0 recent introduced a new routing module to move shortest path solving out of the distance module. Routing functionality has been historically distributed across the distance, speed, and utils_graph modules. We should move it all into the routing module. The former distance.shortest_path and distance.k_shortest_paths functions were already moved accordingly in v1.7.0, with a FutureWarning. The speed module's functions should do the same, as should utils_graph.route_to_gdf.

The utils_graph.remove_isolated_nodes and utils_graph.get_largest_component functions should move to the truncate module, which is their most natural home.

Finally, we should move the utils_graph module's get_digraph, get_undirected, graph_to_gdfs, and graph_from_gdfs functions to a new convert module that houses data type converters.

[gboeing]

Streamlining work in #1148. Deprecation work in #1146.

[gboeing]

The first pre-release OSMnx v2 beta has been released. Testers needed! See #1123 for details.