Switch new_and_build() to spawn_batch() after the BundleBuilder pattern is added if possible

[TheLeonsver1]

like the title says, if all goes well and we only use .spawn_bundle() and nothing else per tile entity In new_and_build(), we should have very good perf, but if and when BundleBuilder(bevyengine/bevy#2157 (comment)) would be added,
if it plays well with spawn_batch() we should get even better perf because that would mean only one memory allocation for entities per layer if I understand correctly.

[TheLeonsver1]

Until then, We decided to try and divide new_and_build() to new_and_build_flexible() and new_and_build_rigid() or something like that,
new_and_build_rigid() would be the much faster(1.6mil entities in 2 sec) version at the cost of flexibility, you would have to return the same bundle type for every tile

new_and_build_flexible() would be much slower(1.6mil entities in 24 sec) but you could spawn any bundle you'd like

[StarArawn]

No longer relevant with the new API.