fix #2541, scale circles in pitch views

[ansis]

fix #2541

Based on the comments in the old code the old the behaviour was intentional but I think the behavior expected in #2541 is better.

👀 @lucaswoj

[jfirebaugh]

Sounds good to me. I guess both symbols and circles should have a style property that controls this. Something like "{icon,text,circle}-pitch-scaling": "{perspective,none}", with default "perspective".

[lucaswoj]

LGTM! 🚢

[jfirebaugh]

Followups:

• add test case for circles with pitch mapbox-gl-test-suite#87
• Port pitched circle rendering from gl-js mapbox-gl-native#5006