Add hot reload apply changes API: AssemblyExtensions.ApplyUpdate

[mikem8361]

Issue: #45689

Currently Windows only: there will be another PR to enable this API on Linux/MacOS.

The Hot reload API will fail if debugging or if the module isn't editable.

[ghost]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, to please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

[ghost]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[ghost]

Tagging subscribers to this area: @tommcdon
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Issue: #45689

Currently Windows only: there will be another PR to enable this API on Linux/MacOS.

The Hot reload API will fail if debugging or if the module isn't editable.

Author:	mikem8361
Assignees:	mikem8361
Labels:	area-Diagnostics-coreclr, new-api-needs-documentation
Milestone:	-

[jkotas]

Any tests to add?

[mikem8361]

We (Aleksey and I) are going to work on some tests. It will take a while to put them together and I didn't want to hold up getting in API so the dotnet-watch tooling (@pranavkm) can start using it.

[noahfalk]

I anticipate we'll continue looking into the debugger interaction and error handling, but if the code as-is helps unblock anyone it seems like a fine starting point.

[noahfalk]

fyi @davidwrighton

[jkotas]

We (Aleksey and I) are going to work on some tests.

It should be straightforward to add basic tests that verify at least some of the error handling as part of this PR.

src\libraries\System.Runtime.Loader\tests is a good place to add tests like that.

[jkotas]

Nit: AssemblyExtensionsTest.cs may be a better name for this file. The convention is to use the same name for the file and the main type in the file.

[jkotas]

Thanks