Add `many_entities_mut` function variants to `DeferredWorld`

[ItsDoot]

What problem does this solve or what need does it fill?

The immutable get_many_entities family of functions are accessible on DeferredWorld thanks to it derefing to &World. The mutable variants, however are not made available through the deref, and are not explicitly defined on DeferredWorld itself.

What solution would you like?

Implement these functions explicitly on DeferredWorld:

• many_entities_mut
• get_many_entities_mut
• get_many_entities_dynamic_mut
• get_many_entities_from_set_mut

[ItsDoot]

Was implemented in #15614 for 0.15.