fix: popup glitches caused by long calculations

[euaaaio]

Contribution checklist

Brief description

When we open a popup, fitPopupPositionedElement is called several times for multiple reasons, which calculates the position of the popup on the screen:

1. Once after the DOM element is rendered and we have the reference.
2. Twice after dispatching the changeContent event from the CreateIssue component.
3. Once after calling resizeObserver from PopupInstance.

The problem is that we get the popup sizes too late, just from resizeObserver. This causes incorrect calculations of the left: calc(50% - -0.5px) parameter.

I suggest setting the initial sizes as soon as the DOM element is ready.

Screencast

bold-fixed-issue-popup-glitches.mov

Checklist

• - UI test added to added/changed functionality?
• - Screenshot is added to PR if applicable ?
• - Does a local formatting is applied (rush format)
• - Does a local svelte-check is applied (rush svelte-check)
• - Does a local UI tests are executed UI Testing
• - Does the code work? Check whether function and logic are correct.
• - Does Changelog.md is updated with changes?
• - Does the translations are up to date?
• - Does it well tested?
• - Tested for Chrome.
• - Tested for Safari.
• - Go through the changed code looking for typos, TODOs, commented LOCs, debugging pieces of code, etc.
• - Rebase your branch onto master and upstream branch
• - Is there any redundant or duplicate code?
• - Are required links are linked to PR?
• - Does new code is well documented ?

Related issues

Resolves #4510

Contributor requirements

• - Sign-off is provided. DCO
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