drag & drop: fix dragging Mac screenshots into galleries

[latter-bolden]

This seems to just have been an issue with spaces in the filename as expected. Uploading screenshots on Mac should now work in Safari.

While testing this, I noticed a regression with the drag & drop fix from the other day as well. There's a long outstanding bug with handling a key dragleave event property in Safari which was causing the drag hover state to flicker or fail. This PR also smuggles in a way to combat that while leaving in place the fix for other browsers.

Worked locally against a self-hosted ship in Safari & Chrome. Whoever tests this, please verify drag & drop works in both gallery and chat contexts on both browsers.

Fixes LAND-1446

PR Checklist

• Includes changes to desk files
• Describes how you tested the PR locally (test ship vs livenet)
• If a new feature, includes automated tests
• Comments added anywhere logic may be confusing without context

[latter-bolden]

Note: this will need to be included in the next release since this patches the other D&D fix which is already on staging.

[linear]

LAND-1446 galleries: macOS default screenshot filename doesn't work in galleries

[arthyn]

code lgtm

[arthyn]

@latter-bolden you might have to rebase if we're going to point at staging

[latter-bolden]

Yep, should be in sync with staging now.

Was also confirming multiple drop zones works as expected, behavior seems to be in line with livenet 👍

[arthyn]

@mrozanski going to deploy this to binnec since this fixes an issue introduced by one of the earlier drag fixes.