BL-15657 replace ElementQueries to fix origami bug

[nabalone]

This change is 

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[JohnThomson]

@JohnThomson reviewed 5 files and all commit messages, and made 1 comment.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @nabalone).

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a discussion (no related file):
It's elegant that you've replaced an obsolete library with modern CSS, but I can't spot what actually fixes the bug.

[nabalone]

@nabalone made 1 comment.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @JohnThomson).

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a discussion (no related file):

Previously, JohnThomson (John Thomson) wrote…

It's elegant that you've replaced an obsolete library with modern CSS, but I can't spot what actually fixes the bug.

We had been relying on ElementQueries to add min-height and min-width attributes to the split-pane-container-inner, which would then make the css rules apply. The bug occurred because ElementQueries was not adding those attributes in certain specific cases, I didn't investigate why. But now with the container queries, the css rules should apply any time the split-pane-container-inner is the specified size

[andrew-polk]

Should this target 6.3?

[nabalone]

Oops yes fixed

@nabalone made 2 comments.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @JohnThomson).

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a discussion (no related file):

Previously, nabalone (Noel) wrote…

We had been relying on ElementQueries to add min-height and min-width attributes to the split-pane-container-inner, which would then make the css rules apply. The bug occurred because ElementQueries was not adding those attributes in certain specific cases, I didn't investigate why. But now with the container queries, the css rules should apply any time the split-pane-container-inner is the specified size

Oh, I see, I forgot to explain the problem! The (+) buttons for creating a new split are positioned with css which assumes that vertical-adders has a reasonable size and then we can do I think it was position: absolute; top: 10px or something like that to position them. But when the aforementioned css rules were unexpectedly not applying, the result was that vertical-adders got height:0, so then what was supposed to be the top (+) button with position: absolute; top: 10px ended up on bottom and the bottom (+) button ended up on top and so they would create unexpected origami splits.

[JohnThomson]

@JohnThomson resolved 1 discussion.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @nabalone).

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