fix typos present in '@theia/core'

[justin8502]

Issue: #6899

What it does

• fixes various typos throughout the codebase.

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the review guidelines

[justin8502]

Still figuring out how merges work. Reset fork to point to upstream, then created a branch from fork with changes for this issue (previously i was just pushing to master).

[vince-fugnitto]

The changes look good to me! 👍

Thank you for your contribution, I understand that working off forks may be confusing at first but there should be some good articles about successfully contributing to open-source using forks :)

For example, the following article describes the usual steps when working in open-source with forks in an easy to convey matter.

[vince-fugnitto]

The branch does look to be in a weird state however as it cannot be rebased safely:

Perhaps follow the general guide described in the article I mentioned.

[justin8502]

Looking into it.

[vince-fugnitto]

Thank you for the changes! 👍