Fix dynamic callback method detection

[shadyvb]

Fixes #1468.

Fixed the dynamic callback locating routine by removing the hyphen as a valid function name character.

Checklist

• Project documentation has been updated to reflect the changes in this pull request, if applicable.
• I have tested the changes in the local development environment (see contributing.md).
• I have added phpunit tests.

Release Changelog

• Fix: Fixed the dynamic callback locating routine by removing the hyphen as a valid function name character.

Release Checklist

• This pull request is to the master branch.
• Release version follows semantic versioning. Does it include breaking changes?
• Update changelog in readme.txt.
• Bump version in stream.php.
• Bump Stable tag in readme.txt.
• Bump version in classes/class-plugin.php.
• Draft a release on GitHub.

[delawski]

@shadyvb Thanks for that fix 🙌

I've changed the target branch to develop since we'd like to release this update as part of the upcoming 4.0.1 release. All of my comments are just about that. I'll try to address them myself, directly in GitHub, so that we're clear right away.

[delawski]

Cleanup after resolving merge conflicts with develop directly in GH.

[delawski]

The Lint and Test task succeeded so I'm merging the PR to develop now. Thanks again, @shadyvb!