Integrate bevy_picking support

[spectria-limina]

bevy_mod_picking, which previously implemented egui support in the bevy_picking_egui crate, now has been integrated into Bevy 0.15.

As a result, bevy_mod_picking and its associated crates are deprecated, and support can now exist in egui proper anyway.

Please important the picking library for egui so that it can continue to be used in 0.15.

[vladbat00]

Hi! Thank you for the issue, this is planned. Though if anyone wants to port the functionality and create a PR themselves, it's welcome as well (as I have quite limited free time myself).