Implementing autocomplete on EuiComboBox

[mpRegalado]

Description

For the country selector in the cloud console, the component ComboBox was used.
This had a feature where beginning to type the name of a country would select the first matching option.
In order to achieve this, the parameters passed to ComboBox's onSearchChange prop were altered from
(searchValue: string, hasMatchingOptions?: boolean) => void
to
(searchValue: string, hasMatchingOptions?: boolean, matchingOptions?: EuiComboBoxOptionOption<T>[]) => void
and an onSearchChange function was developed to manually select the first option of the array matchingOptions whenever the searchValue changed.

Proposed solutions

Add an autocomplete prop

This functionality could come by default from the component itself. Setting autocomplete to true would automatically select the first matching option.

Restore the matchingOptions parameter

Since onSearchChange only shows whether there was a match but not which results matched, adding this parameter to the function would allow for custom behaviors such as the autocomplete