frontend: Replace implicit "=" with "this"

[RytoEX]

Description

Replace implicit "=" with "this".

Motivation and Context

Follow-up to #13320. Required for moving to C++20 or newer.

How Has This Been Tested?

Compiled locally on Windows 11.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

• Code cleanup (non-breaking change which makes code smaller or more readable)

Checklist:

• I have read the contributing document.
• My code has been run through clang-format.
• My code follows the project's style guidelines
• My code is not on the master branch.
• My code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.