Improve top of pagination scroll panel gap

[t3chguy]

Fixes element-hq/element-web#20594
Fixes element-hq/element-web#20896

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Here's what your changelog entry will look like:

🐛 Bug Fixes

• Improve top of pagination scroll panel gap (#8030). Fixes Thread panel doesn't handle window resizing element-hq/element-web#20594 and Extra space (gap) above messages element-hq/element-web#20896.

Preview: https://pr8030--matrix-react-sdk.netlify.app
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[codecov]

Codecov Report

Merging #8030 (316c91c) into develop (9082e07) will decrease coverage by 0.01%.
The diff coverage is 80.00%.

@@             Coverage Diff             @@
##           develop    #8030      +/-   ##
===========================================
- Coverage    26.66%   26.65%   -0.02%     
===========================================
  Files          862      862              
  Lines        51954    51940      -14     
  Branches     13159    13156       -3     
===========================================
- Hits         13854    13843      -11     
+ Misses       38100    38097       -3     

Impacted Files	Coverage Δ
src/components/structures/ScrollPanel.tsx	31.97% <80.00%> (-1.83%)	⬇️

[germain-gg]

This extra gap was there on purpose, because of https:/matrix-org/matrix-react-sdk/blob/develop/docs/scrolling.md#bacat-bottom-aligned-clipped-at-top-scrolling which is why I had not touched it yet.

Not entirely sure whether this is not extraenous or not

[t3chguy]

This extra gap was there on purpose

I know that, this draft is a playground to try a different approach as the hiding of the scrollbar is never going to solve the problem of the scrollbar sometimes being hidden whilst things are off-screen already.

[turt2live]

lgtm so far - the codeowners review can't be removed, and all the stats think this is in a queue, so giving it a review now. Happy to re-review if/when ready.