[BuildSystem] Add support for content exclusion patterns

Question

• Moves BuildValue string list into a reusable data structure
• Adds support for 'content-exclusion-patterns' in the manifest for directory nodes
• Filters exclude items from consideration when calculating directory signatures
• Implements generic binary coding support for BuildKeys

该提问来源于开源项目：apple/swift-llbuild

Answer 1

-ci please smoke test