Allow deletion of typed-in operators

[Northurland]

Problem Statement
In the current version of Calculator, if you typed in an operator, you cannot delete it. This will cause significant inconvenience, especially when dealing with rather complicated expressions, since you may have to discard the done part of the expression due to the wrong operator and type everything again from the beginning.

Adding the requested feature will greatly improve convenience.

Evidence or User Insights
Many scientific calculators, such as the Casio fx-991ES PLUS, support such feature; also, you can easily find online calculators doing so.

Proposal
If there is an operator at the end of an expression (like what is shown in the picture below,)

the user should be able to delete it by backspace on their real keyboard or by the deletion button on the calculator GUI.

Goals
(the same to what mentioned in 'proposal'.)

Low-Fidelity Concept
I think a GIF or a video will explain this perfectly. However, I don't get one.

Requested Assignment
I'm just suggesting this idea. I don't want to implement it.
(Actually I really want to implement it, but I am completely not able to)

[MicrosoftIssueBot]

This is your friendly Microsoft Issue Bot. I've seen this issue come in and have gone to tell a human about it.

[ghost]

Thanks again for submitting your idea! However, after reviewing this pitch more closely, we do not believe it is a great fit for the product at this time. Thank you for your contribution to Calculator!

[grochocki]

This is similar enough to #163 that we would like to treat it as a duplicate. Let's continue the conversation there on how best to allow editing/deletion of typed-in operators.