gui(send): display max calculated amount w/ 8 decimals

[pythcoiner]

fixes #1424

[jp1ac4]

It might look even nicer if you could use the amount_as_string function:

liana/gui/ui/src/component/amount.rs

Line 42 in ff968ea

fn amount_as_string(a: Amount) -> String {

There would be some inconsistency with non-MAX recipients, but it might still look fine as those other amounts are editable. Perhaps later we could use this same formatting for all recipients somehow.

[pythcoiner]

done, ideed it's better.

[edouardparis]

utACK 7ab6d05