"Subtract fees from amount" should show the final payment amount

When sending a new transaction, there is a checkbox option to "Subtract fees from amount". This is a good option to have, and is the default when you 'send max' when you are emptying your entire wallet.

In this case, the fee must naturally be deducted from your max funds. There is a small gray text link which says "Calculate estimated fee" which is good, but I think this should be done automatically whenever this checkbox is checked, and there should be a display with what the final txn amount will be.

Easier to explain with pictures:

Current:


Requested (green minus red equals blue):


And then that white box could update automatically as you drag the fee slider.

PS: the RBF checkbox is overlapping that "Coin Selection" expand button... might be because of scaling issues, i'm on 125% scaling in Windows

Start by locating the transaction-send form and the controls labeled "Subtract fees from amount" and "Calculate estimated fee". Trace how the fee slider and estimated fee currently affect the transaction amount. Done means the estimate runs automatically when subtraction is enabled, the final transaction amount is displayed and updates with the fee slider, and the reported RBF/Coin Selection overlap is investigated.

Written by the indexing model from the issue text.