Problem Statement
Expressions in the history cannot be edited.

Evidence or User Insights
This is a regression from the Win32 app. Requested by #150 and part of #139. I am pretty sure it used to be in Feedback Hub too, but that seems to have been deleted now.

Proposal
When adding a larger number of numbers (e.g. several invoices) and a mistake is discovered, the user now has to re-enter everything again. This proposal allows them to correct the isolated error within longer expression.

Goals
User can fix errors and/or typos in past computations.

Non-Goals
This is not a symbolic evaluation proposal, surrounding history entries are not affected by edits in the current one.

Low-Fidelity Concept
While Win32 calculator allowed expressions in-place, adding Edit item to the current Delete item in the history context menu would do. The expression would then turn into a text box.

(An alternative yet still enabling solution would be to introduce Copy to clipboard on the history items. The user could then fix the expressions out of the app and paste back as new ones.)