feat(pickers): display preview title at the same position as results title for bottom_pane layout

[folliehiyuki]

Description

Here is the current behavior of bottom_pane layout:

• When prompt_position = 'bottom'. Results and preview title are both at the top:

• When prompt_position = 'top' (default). Preview title is displayed at the top, while results title is at the bottom (pretty out of place):

And here is how it looks with this change:

This is a really small change for the position of the preview title of bottom_pane layout. I know the bottom_pane layout function can be overridden within my personal config, but I think this should be the default for consistency, considering that all the other layouts display the titles at the same position (normally at the top of the popup).

Type of change

A subjective aesthetics change.

Checklist:

• My code follows the style guidelines of this project (stylua)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (lua annotations)

[Conni2461]

Thanks :)