Fix build.

I forgot to save buffer, build, then save, then committed :(
[sdb] Fix decoding of nested structs. Fixes #14942.
Add some "new in 4.0" API regarding build event args.
[Mono.Tuner] Remove unused field.
Revert "Allow workitems to startup faster and reduce polling thread interval in the threadpool."

This commit is causing unbound growth in the number of threads for a series of workloads.

It's leading a sgen test to crash with 800 tp threads around, which doesn't make sense on a
4 cores system with default TP configuration.

This reverts commit 3c347d5d3a9c58666ef33c96e28a16c751e59619.
implement some "new in 4.0" build event args types.
Add ConsoleLoggerTest and fixed implementation to match .NET implementation.
Fix potential NRE and give better output for fields and some types
Anonymous method with this access inside an iterator needs to initialize captured this field from iterator's copy. Fixes #14926