Refactors theming app - part 1

[fsamapoor]

Summary

Following previous PRs taking advantage of PHP8's constructor property promotion, I have also made the required adjustments to the classes in the theming app.

I decided to split the changes into multiple PRs to make reviewing the changes easier.

The improvements in this PR include:

• Using PHP8's constructor property promotion
• Adding return types
• Removing redundant docblocks
• Replacing magic numbers with readable constants

Checklist

• Code is properly formatted
• Sign-off message is added to all commits

[github-actions]

Hello there,
Thank you so much for taking the time and effort to create a pull request to our Nextcloud project.

We hope that the review process is going smooth and is helpful for you. We want to ensure your pull request is reviewed to your satisfaction. If you have a moment, our community management team would very much appreciate your feedback on your experience with this PR review process.

Your feedback is valuable to us as we continuously strive to improve our community developer experience. Please take a moment to complete our short survey by clicking on the following link: https://cloud.nextcloud.com/apps/forms/s/i9Ago4EQRZ7TWxjfmeEpPkf6

Thank you for contributing to Nextcloud and we hope to hear from you soon!

[DaphneMuller]

hi, I've asked my colleagues who would be the best reviewer for this one!

[fsamapoor]

hi, I've asked my colleagues who would be the best reviewer for this one!

Hello @DaphneMuller,

Thank you for your message!

I have 50 PRs merged in, and I know eventually, someone will come, and we'll make it somehow. However, from a broader perspective, I wanted to share some thoughts on how you could encourage more people to contribute to the ecosystem.

[DaphneMuller]

@fsamapoor I'll contact you by mail to continue that discussion 😊

[come-nc]

All good but might as well treat $l10n the same as the others.

[come-nc]

Suggested change

	IL10N $l,
	private IL10N $l10n,