Lazily allocate the screenmap bitfield

Description

The screenmap does not always end up being useful, when zoomed in there is actually nothing so small to fit a pixel. Yet, the allocation of the bitfield happens in the constructor, and can cause a visible slowdown in cases where it's a significant allocation point, e.g, while computing vector tiles in GeoServer.
Making it lazily allocated saves GC some work.

Environment

None

Assignee

Andrea Aime

Reporter

Andrea Aime

Triage

None

Fix versions

Priority

Medium
Configure