In Add/remove currencies modal, need to click before typing to filter/select currencies

[haszari]

Describe the bug

The Add/remove currencies modal allows filtering by text, e.g. type au to quickly select ⇒ add $AUD.

However, the user needs to click in the Search currencies box for this filtering to work.

To Reproduce

1. Enable multicurrency.
2. Go to > WooCommerce > Settings > Multi-currency.
3. Click Add/remove currencies
4. Start typing.

Actual behavior

Nothing happens.

Expected behavior

Two options:

1. Focus the search box on load.
2. Catch characters/typing anywhere in the modal and filter.

(1) seems quickest and easiest to implement.