fix(core/panes): expanded and slot error

[jul-lam]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build (yarn build) was run locally and any changes were pushed
• Unit tests (yarn test) were run locally and passed
• Visual Regression Tests (yarn visual-regression) were run locally and passed
• Linting (npm lint) was run locally and passed

Pull request type

Please check the type of change your PR introduces:

• Bug fix
• Feature
• Refactoring (no functional changes, no API changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

When a pane within a layout is initially expanded, it closes upon rendering. Some icons were not displayed correctly, and some paddings were incorrect following certain animations. Moreover, a display issue arose when changing the slot for a pane that was in the process of closing (during its animation phase).

GitHub Issue Number: #1108

What is the new behavior?

The pane now remains expanded. In addition, the minor UI issues have been resolved, along with a problem that occurred when changing a slot while a pane was closing.

Does this introduce a breaking change?

• Yes
• No

Testing

Manual tests.

Other information