[Feat]: Support for Brightness and Alpha channels in sp-color-slider

### Code of conduct

- [X] I agree to follow this project's code of conduct.

### Impacted component(s)

sp-color-slider

### Description of the requested feature

Need to use the brightness and alpha sliders in Color Picker for my project.

Currently, we're using React Spectrum's ColorSlider and we're encountering an issue where when the slider is wrapped in an overlay-trigger and sp-popover to display the contents inside. If we press and hold on the color slider and drag it outside the popover, the popover gets closed and it doesn't happen if we use sp-color-picker.

### Mockups or screenshots

### Implementation notes or ideas

Can follow React Spectrum's component ColorSlider's implementation.

Start by locating the sp-color-slider component and compare its implementation with React Spectrum's ColorSlider. Verify the requested brightness and alpha slider behavior, including dragging beyond an sp-popover without closing it; done means both channels are supported and the reported interaction works.

Written by the indexing model from the issue text.