User experience when sending to Stellar wallet with autogenerated memo

Hi, this is a follow up on #19388
It works great, resolves memo and doesn't let user override it.

However when you opt-in for a path_payment, there is still an editable field for memo

Thankfully, putting anything there leads to an error

But I'm sure you can do better than scaring users away with error messages by not allowing to edit this field.

Start by reproducing the Stellar wallet send flow with a path_payment selected and compare it with the ordinary send flow shown in the issue screenshots. Trace where the memo field is rendered and validated; done means the autogenerated memo cannot be edited in this flow and users are not led to the existing error.

Written by the indexing model from the issue text.