(core) Fix css issue with tooltip in filter menu on safari

Summary:
Small glitch on safari: when we show behavioural tooltips the content
of the tooltip is first added to the parent of the target elem, then
we set tooltip's container positioning to absolute which normally causes recompute
of the layout. But in safari it doesn't, hence the button shows as if
the tooltip was still in there, as a sibling.

Diff fixes that issue by forcing positioning to absolute on the tooltip container.

{F68474}

Test Plan: Should not break anything.

Reviewers: georgegevoian

Differential Revision: https://phab.getgrist.com/D3802

app/client/components/modals.ts

@@ -323,7 +323,7 @@ const cssBehavioralPromptModal = styled('div', `
   border-radius: 4px;
 
   animation-duration: 0.4s;
-  position: relative;
+  position: absolute;
 
   &[x-placement^=top] {
     animation-name: ${cssFadeInFromTop};