Fix toolbars positionning in IE11

[youknowriad]

This PR fixes a visual glitch in ie11 where toolbar segments in block toolbars appear one per line instead of part of the same "line".

I'm interested in testing this PR in other browsers to ensure there's no unwanted side-effect.

Testing instructions

Test block toolbars in Chrome/Firefox in several situations/alignments... and ensure it displays properly.

[jasmussen]

Right off the bat it has a cost for non IE. This is Chrome:

We have done some tricks in other code like this:

.block-editor-block-toolbar__slot {
	// Required for IE11.
	display: inline-block;

	// IE11 doesn't read rules inside this query. They are applied only to modern browsers.
	@supports (position: sticky) {
		display: inline-flex;
	}
}

[jasmussen]

What am I looking for in IE11? This is after setting it back to flex.

[youknowriad]

@jasmussen try to the image block instead (upload an image and check the toolbar)

[jasmussen]

I can't test anymore because my virtualbox started crashing hard, so hard the mac reboots :(

@jorgefilipecosta can you look?

However as noted, the inline-flex rule breaks it for me in Chrome. You might want to do the "@supports" trick.

[jorgefilipecosta]

Hi @youknowriad, I'm also noticing the problem @jasmussen referred to in other browsers.
This problem is complex:
We have this I.E specific toolbar styles:

 .block-editor-block-toolbar__slot {
-	// Required for IE11.
-	display: inline-block;
-
-	// IE11 doesn't read rules inside this query. They are applied only to modern browsers.
-	@supports (position: sticky) {
-		display: inline-flex;
-	}
+	display: inline-flex;
 }

If we remove and use inline-flex even on IE things start to work well in some blocks e.g: media & text but the toolbar of paragraphs starts breaking on IE.

The fix you proposed seems an improvement on IE (there is only some unalignment) maybe we can target the fix for IE only?

[youknowriad]

The fix you proposed seems an improvement on IE (there is only some unalignment) maybe we can target the fix for IE only?

Yes, if we don't find anything better, we should do that.

[youknowriad]

I only applied the fix to IE11, I think now it's decent in all browsers.

[jorgefilipecosta]

LGTM 👍