Adds support for new iOS 13 traits

[ay8s]

Adds userInterfaceLevel, accessibilityContrast and legibilityWeight available in iOS 13.

While looking into this I spotted that NSStringFromASPrimitiveTraitCollection (ASTraitCollection.mm) is inserting a nil value for preferredContentSizeCategory under iOS 13 when rotating a device. Similar to what we were seeing here... #754

We could create a AS_NSString method to handle it or check if it doesn't exist and just pass add UIContentSizeCategoryUnspecified.

[ghost]

🚫 CI failed with log

[nguyenhuy]

Note to reviewers: Blocked by Xcode 11 GM and CI upgrade.

[noamalffasy]

@nguyenhuy Xcode 11 GM is out now

[rahul-malik]

@ay8s - Hey just checking in on this since it'll be helpful for folks building for iOS 13. Can you rebase / resolve conflicts?

[ay8s]

@rahul-malik Away on a retreat this week so can take a look next week. Feel free to pick up if you need it sooner.

[rahul-malik]

@ay8s - Ping :)

[nguyenhuy]

FYI, I think this PR causes the podspec linting CI job to fail:

- ERROR | [Texture/Core, Texture/PINRemoteImage, Texture/IGListKit, and more...] xcodebuild: Returned an unsuccessful exit code. You can use `--verbose` for more information.

- ERROR | [Texture/Core, Texture/PINRemoteImage, Texture/IGListKit, and more...] xcodebuild:  /Users/runner/runners/2.163.1/work/Texture/Texture/Source/Details/ASTraitCollection.h:51:3: error: 'UIUserInterfaceLevel' is unavailable: not available on tvOS

- ERROR | [Texture/Core, Texture/PINRemoteImage, Texture/IGListKit, and more...] xcodebuild:  /Users/runner/runners/2.163.1/work/Texture/Texture/Source/Details/ASTraitCollection.h:155:22: error: 'UIUserInterfaceLevel' is unavailable: not available on tvOS

- ERROR | [tvOS] [Texture/TextNode2] xcodebuild:  /Users/runner/runners/2.163.1/work/Texture/Texture/Source/Details/ASTraitCollection.h:155:22: error: 
- NOTE  | [tvOS] [Texture/TextNode2] xcodebuild:  note: 'setInsetsLayoutMarginsFromSafeArea:' has been marked as being introduced in tvOS 11.0 here, but the deployment target is tvOS 9.0.0

https://github.com/TextureGroup/Texture/runs/371568518

https://github.com/TextureGroup/Texture/commit/3c8acbc1de9c54b60a020464d5bc777e9a4a3181/checks/371568518/logs

P/S: Perhaps we should run podspec lint on every pull request to catch issues earlier? Right now it's run on master only because the task is really slow.

[jparise]

Perhaps we should run podspec lint on every pull request to catch issues earlier? Right now it's run on master only because the task is really slow.

Good idea. I think it would be worth it.