Feature/time provider

[trejjam]

Use TimeProvider instead of DateTime.Now

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This PR adds TimeProvider for .net8+ targets. It's done as an additional property, TimeProvider, on Descriptor/Parameter classes.

Description

I added TimeProvider to nearly all usages of DateTime.Now. Some were too difficult to add (BC Break).

Fixes #2572

[trejjam]

Hi. Can you take a look at this? I would love to have some feedback :)

[alexmurari]

@pmaytak This PR is a follow-up of the previous one you reviewed. We would appreciate your review here too.

[brentschmaltz]

I wonder if there are other properties on the TimeProvider we would use besides UtcNow.

[brentschmaltz]

Why a new define and not just NET8+

[trejjam]

It is not a big reason but a matter of personal preference. It allows easy integration of Microsoft.Bcl.TimeProvider if requested.

If you prefer NET8_0_OR_GREATER, I will change it.

[trejjam]

There is also available timezone info, GetElapsedTime, a Timer, ...

I prefer to use these in a following PR.

[jennyf19]

@iNinja and @FuPingFranco (@brentschmaltz ) are you considering this with the changes you are doing to validationParameters?

[alexmurari]

This pull request already laid some groundwork for enabling TimeProvider for token validation. It's internal for now...