sl-select doesn't update label if sl-menu-item label changes

[bunesk]

Describe the bug

If you have a sl-select with some sl-menu-item within and the label/slot of the selected sl-menu-item changes it won't be updated on the sl-select.

To Reproduce

Steps to reproduce the behavior:

1. Create a SlSelect with some options
2. Change the label of the selected SlMenuItem

Demo

https://codepen.io/buni48/pen/PoOKLbQ

[claviska]

This has been fixed in caaf2b0. I also added a test to prevent regressions.

While fixing this, I was also able to improve performance slightly, as menu items are now cached on slotchange rather than fetched multiple times throughout the component's lifecycle. I'll probably make similar changes to remaining components that follow the same pattern.

[bunesk]

Sounds great. Thank you.