Better handling for undefined icon|text-rotation-alignment

[yhahn]

I believe this addresses the root cause behind #5683.

• Updates GL style spec to remove an explicit default from text-rotation-alignment and icon-rotation-alignment. This value was a lie given that renderers currently derive the default in coordination with symbol-placement
• Update logic in GL native to set the default value for these properties only when they are undefined.

Remaining backlog

• @yhahn Render tests to lockdown expected behavior
• @yhahn Vet style spec change, esp possible effect on GL JS and other integrators
• Review @1ec5 @jfirebaugh

[mention-bot]

@yhahn, thanks for your PR! By analyzing this pull request, we identified @jfirebaugh, @mikemorris and @ansis to be potential reviewers.

[1ec5]

Nit: extra semicolons (3×).

[yhahn]

Quick discussion with @1ec5 -- one possible approach to address the special-caseness of these properties would be to add an explicit enum value to the spec like auto or inherit for text-rotation-alignment, icon-rotation-alignment and text-pitch-alignment.

• Add auto enum value
• Set default value to auto
• Update logic in GL native/JS to handle this appropriately

I'm fairly certain this would be a breaking change though -- styles explicitly using the value auto would not parse (?) with older renderers.

[jfirebaugh]

Yes, I think we need to add auto for all three of these properties, and treat this new value like we would treat the addition of a new style property -- add a row in the spec property support table documenting the minimum versions requirements.

[boundsj]

@jfirebaugh @lbud this file was falling behind so I rebased on top of master. This commit keeps @lbud's latest changes but changes s/bucket->layout/layoutProperties

[jfirebaugh]

Changes here look good. Do we have a test case for the original issue #5683?

[boundsj]

@jfirebaugh a PR for GL JS tests is started and is blocked by mapbox/mapbox-gl-js#3203. We still need to add render tests to this PR.

[jfirebaugh]

Style-spec, test-suite, and gl-js have been updated. Remaining work here is to get the tests passing.

[jfirebaugh]

Two of the icon-rotation-alignment tests are failing due to very slight positioning differences. 😖 I'll finish up tomorrow.