Fix a few typos

[planger]

What it does

This change just fixes a few typos that I came across while working on other tasks.

How to test

The only code-relevant changes are in the names of protected methods in the MemoryProvider class. Unless someone subclassed this class in proprietary code, there isn't really anything this change could break.

Review checklist

• [X] as an author, I have thoroughly tested my changes and carefully followed the contribution guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the code of conduct