reduce the memory consumed by the inflation layer

[facontidavide]

Background

InflationLayer uses a lot of memory for large maps and this memory is never freed.

The image below is the total meory used by our application using a very large map ( 200 MB)

After this change, the change in used memory is dramatic

[doisyg]

Great gains confirmed on A17 with the GXO maps (and a test image).

So 2GB gain on the big GXO map at 0.05 resolution.
Also tested the inflation layer behavior (updates are working) in simulation, all good.
This can now makes its way to nav2 upstream if you want to open a PR @facontidavide

[facontidavide]

This can now makes its way to nav2 upstream if you want to open a PR

ros-navigation#4424