LazyCache is a value type (struct) with a lock inside, that's broken and doesn't work

https://github.com/apple/swift-tools-support-core/blob/dd1717f2d3225dc79c036c6c9e72ed4e48340d83/Sources/TSCBasic/LazyCache.swift#L33 This needs to be converted to a `class` to do what it's supposed to do, currently this is very thread-unsafe.