We previously skipped building/running tool plugins here, which meant that the compiler arguments for a target also missed any generated sources. Use the new `BuildDescription.load` API from SwiftPM to address this. Resolves rdar://102242345.
InternalImportsByDefault
IndexStoreDB
SourceKitLSPServer
build/taskStart
build/taskProgress
build/taskFinish
AsyncQueue<Serial>
SKSupport
LanguageServerProtocolExtensions
PrefixMessageWithTaskEmoji.swift
SKCore
BuildSystemIntegration