Merge topic 'refactor-install'

a23fcc95 cmInstallTargetGenerator: Port to cmGeneratorTarget.
4e41913f cmInstallCommand: Store only a targetName, not a cmTarget.
e5e52970 cmInstallGenerator: Add a Compute() virtual hook.
3ef8aaaa cmInstallCommand: Move the SetHaveInstallRule invocation.
5f662b38 cmScriptGenerator: Remove unused method.
0368552d cmGlobalGenerator: Move QtAutogen handling to Compute().
5edb3354 cmGlobalGenerator: Virtualize the Compute step and override it.
ff1019bf cmGlobalGenerator: Move generation object creation to Compute().
aa2407d8 Xcode: Use allBuild target return value.
610572b7 cmMakefile: Simplify generate-time cmGeneratorTarget creation.
2e94cba3 cmGlobalGenerator: Move FinalizeTargetCompileInfo to Compute().
fb9355c5 cmGlobalGenerator: Return from Compute whether to generate.
29e8b7bf cmGlobalGenerator: Create a new Compute step before generation.
1ef9b2b6 cmGlobalGenerator: Remove the TargetManifest member.
5c14f780 cmGlobalGenerator: Remove unused manifest accessor.
a1209be5 VisualStudio: Skip global targets when processing.
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