Merge topic 'extract-computed-target-properties'

cef59bb8 cmTarget: Implement GetProperty in terms of cmState::Snapshot
0d57b07a cmTarget: Group code for checking written properties together
c3fb0d95 cmTarget: Move sanity checks and computed property access to callers
fa9dbc56 cmGeneratorTarget: Implement cmTargetPropertyComputer interface
848ae2a6 cmTargetPropertyComputer: Template some methods on the Target
a0a720e6 cm{,Generator}Target: Add global generator accessors
637e3f3e cmTargetPropertyComputer: Unify whitelist handling from cmTarget
05251e6d cmTargetPropertyComputer: Move whitelist check from cmTarget
fbf1721c cmTargetPropertyComputer: Extract into new files
390a7d86 cmTargetPropertyComputer: Implement GetProperty without cmMakefile
e32a6bdd cmListFileBacktrace: Add a method to retrieve the Bottom of a snapshot
7863fba1 cmTarget: Extract GetLocation method
8096682e cmTarget: Extract GetSources method
7d57c1a2 cmTarget: Extract location computation methods
a55cac4b cmTarget: Split property computation into separate class
705fcf52 cmTarget: Move IMPORTED check to callers
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