[Select,Combobox,MultiSelect] Add disabled states

[akdetrick]

Add a disabled state to Combobox, Select, and MultiSelect.

Components using DropdownTrigger should be able to take a disabled prop to pass down to DropdownTrigger.

Uncontrolled updates should be disabled when the component has the disabled prop.

Dropdown triggers should be disabled when the component is disabled.

Design

We should use the styling of TextInput in its disabled state as a guide:

Definition of Done

• TextInput has an explicit disabled prop documented
• DropdownTrigger supports a disabled state (see design above)
• Combobox supports a disabled prop (FOLLOW UP: [downshift] Upgrade downshift to v9 #1251)
• Select supports a disabled prop
• MultiSelect supports a disabled prop

Follow up tasks

• Update BANKW-567

[akdetrick]

Screenshots

TokenInput:

In a disabled state, we render the chips without a dismiss button and set the background to primary subdued 10%:

Select:

When disabled, the Select will show current selection (if applicable), and the dropdown indicator will be removed:

MultiSelect:

Disabled styling is basically identical to a disabled TokenInput

[akdetrick]

@Hillary Could you take a quick look at the above and confirm these look right for disabled styling?