[6.0][ScanDependency][canImport] Improve canImport handling in explicit build #74105
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Explanation: Teach dependency scanner to report all the module canImport check result to swift-frontend, so swift-frontend doesn't need to parse swiftmodule or parse TBD file to determine the versions.
Scope: Improve scanner consistency and fix the clang module cross import issue when swift caching is enabled.
Issue: rdar://128067152
Original PR: #73853
Risk: Low
Reviewer: @tshortli
Testing: SWB test and Unit Test