Use non-deprecated Azure Pipelines Ubuntu/Windows pool

[akoeplinger]

ubuntu-16.04 was removed recently (actions/runner-images#3287), bumping to 20.04

win2016 will be removed in March: actions/runner-images#4312, bumping to windows-2019

[akoeplinger]

@echesakovMSFT it looks like the Linux build fails because there's a new RID and this doesn't work with the logic in

jitutils/bootstrap.sh

Lines 73 to 80 in 89c6aba

	# Figure out which version to download. The "RID:" value from "dotnet --info" looks
	# like this:
	# RID: osx.10.12-x64
	info=$(dotnet --info |grep RID:)
	info=${info##*RID:* }
	clangFormatUrl=https://clrjit.blob.core.windows.net/clang-tools/${info}/clang-format

We could either upload a ubuntu 20.04 version to the blob store or download the earlier version, what do you think?

[echesakov]

I think for now we can fix the script by downloading an earlier version.
Actually, I didn't know that the clang-tools blobs use RIDs...

[akoeplinger]

@echesakovMSFT done

[echesakov]

Thanks @akoeplinger