Robustness improvements in the compiler downloader

[kanej]

In Hardhat 3 the compiler downloader has been ported over. It is missing some key robustness features that Hardhat 2 had, and some features we wanted to add to Hardhat 2's version of the compiler downloader.

TODO

• Bring back mutex during multiple compiler downloads
• The downloader and compiler classes were imported but not their tests
• The downloader was changed but not its tests
• Always download both native and wasm builds
• trim down solcjs and keep only the wrapper #6071