Remove async await where not needed

[Henr1k80]

Prerequisites

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Description

Remove async await where not needed.

I am aware that I have changed a lot of files, and it might not make a lot of performance difference in most places, but I wanted to eliminate the horrible await Task.FromResult( from the codebase, so it is never copied again.
Many of the controller methods could be be made sync, but I supposed it would make it fail the signature change check.

[github-actions]

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[AndyButland]

Thanks for the effort on this one @Henr1k80 but I'm afraid we've already had this covered in another PR - #16535 - that we've merged in for Umbraco 16. It could have been in 15 as it's not breaking, but we felt when reviewing it was better for the next major just so we have a longer period for a release candidate just in case something gets missed in implementation or review.

So we will be removing the await Task.FromResult constructs via that, and just live with them in the current version.

Apologies for your wasted work on this one. Do feel free in future to raise an issue suggesting a PR you'll make if you are going to spend a fair bit of time on one - as hopefully then someone will catch it before you embark on something we may not need.