Fix gallery size labels

[mkevins]

Fixes #1792

Related PR

gutenberg: WordPress/gutenberg#19800

Description

This PR fixes the image size option labels in the gallery block settings. The image size options were added for web, but on mobile, the labels were undefined. This resulted in "blank" buttons, and in the beta build for iOS this also resulted in a crash.

How has this been tested?

Tested on Android via WordPress-Android, and iOS via WordPress-iOS:

Steps:

• Create a gallery block with some images
• Tap the gallery
• Tap the gallery settings icon (the gear)
• Tap "Images size"

Expected result:

• The app should not crash
• The image size options should be visible in the menu

Steps:

• Tap one of the image size options (e.g. thumbnail)

Expected result:

The image resolution should change (to a lower quality with thumbnail, higher quality with large or full).

Screenshots

Types of changes

On mobile, the name property in imageSizes is undefined, but label is already set. So this PR defaults to using the label if it is truthy, and falls back to using the name if not.

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[chipsnyder]

Tested in Wordpress iOS and Wordpress Android working as expected

[geriux]

Approved by WordPress/gutenberg#19800 (review)