Fix asset panel folders resizing handle when scrolled down

[Maksims]

Fixes #1277

It seems that there is an inherit issue with PCUI container element, if it is set to be scrollable as well as resizable, then scrollable style is set on the parent element, leading to resizing handle to be overflow-cut.
In Editor other panels, like hierarchy panel have multiple containers - one for resizing, and then inside of it one for scrolling.
This PR does the same - it adds a new container in for resizing, and then container with files for scrolling as before.

Also tested that auto-scrolling when dragging - still works.

This also fixes the horizontal scroll issue, below are two screens before and after the change (green highlight for the screen):

• I confirm I have read the contributing guidelines

[Copilot]

Pull Request Overview

This PR fixes an issue with the asset panel's folders resizing handle being cut off when scrolled down, addressing issue #1277. The problem occurred because PCUI container elements with both scrollable and resizable properties set the scrollable style on the parent element, causing the resize handle to be hidden by overflow.

• Separates resizing and scrolling functionality by creating a dedicated left container for resizing
• Moves the folders container inside the resizing container to handle scrolling independently
• Updates CSS styles to properly position the new container hierarchy

Reviewed Changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
src/editor/assets/asset-panel.ts	Adds new left container for resizing, reorganizes folder container hierarchy
sass/editor/_editor-assets-panel.scss	Updates CSS selectors and styles for the new container structure

Comments suppressed due to low confidence (2)

src/editor/assets/asset-panel.ts:421

• [nitpick] The variable name '_containerLeft' is not descriptive enough. Consider renaming it to '_containerResizable' or '_containerFoldersResizable' to better indicate its purpose as the resizable wrapper for the folders panel.

        this._containerLeft = new Container({

src/editor/assets/asset-panel.ts:29

• [nitpick] The constant name 'CLASS_LEFT' is not descriptive enough. Consider renaming it to 'CLASS_RESIZABLE' or 'CLASS_FOLDERS_RESIZABLE' to better reflect its purpose as the resizable container wrapper.

const CLASS_LEFT = `${CLASS_ROOT}-left`;

[willeastcott]

Great stuff! Your first editor PR in 8 years! 🎉 Thanks!

[Maksims]

Great stuff! Your first editor PR in 8 years!

I needed a bit of rest 🙏

[willeastcott]

I needed a bit of rest 🙏

LOL. Glad you're back. ❤️