Added task assembly location to TaskStartedEventArgs

[MichalPavlik]

Fixes #9290

Context

TaskStartedEventArgs now contains AssemblyName of the assembly that implements the task.

Changes Made

Adding full assembly name to event and propagating the value from upper layers. ITaskExecutionHost interface was removed.

Testing

Manual testing for setting the value. Unit test for serialization

Notes

[MichalPavlik]

@ladipro, is this comment still valid? I would remove the interface as part of this PR
https://github.com/dotnet/msbuild/pull/9948/files#diff-ddd6688a0412c50705a77043f780edaec5bbb785f71dbbb1c4126a7aa8c9fcb7L45

[ladipro]

The interface is internal and has only one internal implementation. So it looks like the comment is still valid.

[MichalPavlik]

I had same opinion, but I wanted to check if there is a plan to implement additional execution host(s)... for whatever reason :)

[ladipro]

I've left a couple of inline comments.

[JanKrivanek]

Overall looks good.

I'd want the BuildEventArgsReader to be backwards compatible before I signoff.
Plus don't forget to update the same class in Viewer repo as well (or create task in viewer repo for that)

Having the diverging assembly path logging handled here or tracking item created would be nice as well.

[MichalPavlik]

... Plus don't forget to update the same class in Viewer repo as well (or create task in viewer repo for that)

Having the diverging assembly path logging handled here or tracking item created would be nice as well.

@JanKrivanek, I created tracking issue for the viewer: KirillOsenkov/MSBuildStructuredLog#771

[KirillOsenkov]

I think we need the viewer support ready and merged first, then merge this PR.