select: label accessibility

[nikkimk]

Description of the issue*

• pf-listbox should have an accessible label

• pf-select's toggle button text should not be the item selected but something more descriptive

• Note this breaks with upstream API but is more accessible.

Impacted component(s)

• pf-listbox
• pf-select

Steps to reproduce

1. Go to Select documentation
2. Inspect the first example.
3. Check the accesisbility tree.

Expected behavior

Listbox and toggle button should have descriptive labels.

[bennypowers]

pf-select's toggle button text should not be the item selected but something more descriptive

we can add an aria-label to the button, but the select element shouldn't look or behave differently to upstream