IExternalScopeProvider can now be injected (#2409)

[TheXenocide]

• Added IExternalScopeProvider parameter to LoggerFactory to allow injection.
• Registers default implementation if not otherwise registered.

Addresses #2409

Note: this is currently based on the release/3.0 branch since I verified that it would solve the problems I'm having with the current stable release. I can rebase to 3.1 if necessary.

[dnfclas]

All CLA requirements met.

[davidfowl]

Note: this is currently based on the release/3.0 branch since I verified that it would solve the problems I'm having with the current stable release. I can rebase to 3.1 if necessary.

Best to assume that everything goes into master. There's an approval process for things to make it into 3.1 and this doesn't meet the bar.

[TheXenocide]

Just so I understand what you mean about 3.1, is that meaning our team definitely won't be able to use IExternalScopeProvider until .NET 5.0? I don't mind rebasing to master, just wondering what the implications are for our adoption schedule and what kinds of requests do meet the bar for 3.1 (I'm guessing this just means the scope of work is already finalized)? Other than that, one thing this PR does is mark a method as virtual, though I'm wondering if that's not worth discussing further (possibly in the original feature request; not really sure where would be more appropriate)? Thanks for your time.

[davidfowl]

Just so I understand what you mean about 3.1, is that meaning our team definitely won't be able to use IExternalScopeProvider until .NET 5.0? I don't mind rebasing to master, just wondering what the implications are for our adoption schedule and what kinds of requests do meet the bar for 3.1 (I'm guessing this just means the scope of work is already finalized)? Other than that, one thing this PR does is mark a method as virtual, though I'm wondering if that's not worth discussing further (possibly in the original feature request; not really sure where would be more appropriate)? Thanks for your time.

Yes that's correct. The 3.1 bar is extremely high, you can think about it like a patch for 3.0 (mostly bug fixes and critical feedback from 3.0). This is a new feature that introduces a new API which needs to be reviewed and signed off and doesn't meet that bar.

[TheXenocide]

global.json in master is set to .NET 5 Alpha already, which I haven't found anywhere (and I'm not particularly excited about building all of .NET from source just to modify a few lines here and there). Is there guidance for how to work against master?

[TheXenocide]

Okay, found the installer for latest SDK bits

[TheXenocide]

I haven't forgotten about this, but now that we've worked around the issue at the office, any contribution I make will likely be from home (harder to find spare time, but probably better for keeping my build environments isolated since I really don't want to install the preview SDK on my work machine).

[ghost]

As per aspnet/Announcements#411, we are currently migrating components from this repository to other repositories. This PR targets components that have been moved to dotnet/runtime, in the src/libraries directory. If you're still interested in contributing this change, please retarget your PR to dotnet/runtime and reference the original issue discussing the change or bug fix. If you have questions, or need guidance on how to port your change, please tag @dotnet/extensions-migration in a comment and we'll try to help.