[core] Implement text-writing-mode layout property for symbol layer

[alexshalamov]

Brief description

For languages that support vertical writing mode, map designers might want point labels to be rendered vertically. This PR adds implementation for text-writing-mode layout property that controls preferred writing mode. New property value is an array, whose values are enumeration values from a ( horizontal | vertical ) set.

The new property do not enforce orientation of a rendered label and acts merely as a hint, so that:

• label consisting of Latin script characters would be still rendered horizontally, even if "text-writing-mode" : ["vertical"] is specified
• same is applicable for vertical languages, e.g., Mongolian and Manchu, "text-writing-mode" : ["horizontal"] would not affect vertical rendering of a label.

To be done

• Add render tests (branch)
• Select property name
• GL-JS v8 spec documentation (branch)
• Upstream alexshalamov_fix_diff_imports
• Upstream GL-JS branch (alexshalamov_wip_vertical_labels) and pin gl-native upstream gl-gs
• Reduce binary size for the feature (If needed @alexshalamov can follow-up in separate PR)
• GL-JS port (@vakila is working on it)
• Implement support for vertical-latin-upright writing mode
• Implement support for vertical-latin-sideways writing mode
• Add changelog to SDKs

Future work

• Experiment with transitions for variable placement / label orientation switch
• Vertical-only rendering for Mongolian / Manchu
• De-duplicate text-variable-anchor and text-writing-mode array properties, so that layers can be efficiently grouped by layout id.

[fabian-guerra]

Thank you for tackling this. We discussed that changing the return type of textVariableAnchor will require a semver, and for that reason this change will be reverted.

When we add a new enum we also have to provide a round trip conversion to NSValue. See my comment for more info.

[tobrun]

👍 on the android changes.

[1ec5]

Most of the feedback below is about wordsmithing tweaks, probably in the code generation scripts.

In addition to the feedback below, consider adding rendering tests for the following cases:

• Vertical CJK containing RTL Arabic text (example)
• CJK punctuation inside vertical point-placed labels (both left-binding punctuation like periods and right-binding punctuation like opening brackets)
• Multiline vertical CJK containing LTR Latin text

[alexshalamov]

• Vertical CJK containing RTL Arabic text (example)
• CJK punctuation inside vertical point-placed labels (both left-binding punctuation like periods and right-binding punctuation like opening brackets)
• Multiline vertical CJK containing LTR Latin text

@vakila As per yesterday's discussion ^^^ great input from @1ec5 about what kind of tests we might need to add.

[alexshalamov]

@julianrex @fabian-guerra I'm planning to land this PR early next week, please provide your comments, if you have any.

[alexshalamov]

The gl-js port of this PR has already landed, therefore, I'm landing this PR. Issues related to combination of icon-text-fit text-variable-anchor will be addressed in separate PR.