[cashtab] Prevent wheel event for agora price setting input.

Summary:
Price setting should be consistent with the send input box and disable the wheel event, because this
can cause users to scroll down and quickly click list etoken after entering a price, by which time the price has
already changed. Similar cases have occurred several times recently. Since preventing the event doesn't work
here, a safer method of blur (losing focus) was used.

Test Plan: Local demo testing

Reviewers: bytesofman, emack, O1 Bitcoin ABC, #bitcoin_abc

Reviewed By: bytesofman, O1 Bitcoin ABC, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D18085