cmGeneratorTarget: Make GetIncludeDirectories const.
cmTarget: Make custom command accessors API const.

Add specific mutators instead of providing non-const refs.
cmTarget: Make GetTargetSourceFileFlags const.
cmTarget: Make GetInterfaceLinkLibraries const.
cmMakefile: Make IsAlias const.
cmMakefile: Make FindTarget const.
cmGlobalGenerator: Make NameResolvesToFramework const.
cmTarget: Make NameResolvesToFramework const.
cmTarget: Make GetExportMacro const.

The std::string member is only used for memory management.
cmTarget: Trivially make more API const.
KDevelop: Use GetLocation(0) instead of LOCATION property.

This can be migrated to use cmGeneratorTarget later.
Tests: Don't read the LOCATION property from build targets.
Port some of the generator API to cmGeneratorTarget.

Just enough to reach the BuildMacContentDirectory method and the
NeedRelinkBeforeInstall methods.

In the future, those methods can be moved to cmGeneratorTarget.
Add a null check to the generator target accessor.
Merge topic 'constify' into next

1de4dc4 cmTarget: Trivially make more API const.
d42c0ee cmTarget: Make GetExportMacro const.
ae56fe6 cmTarget: Make NameResolvesToFramework const.
261a7ca cmGlobalGenerator: Make NameResolvesToFramework const.
d3e5b5d cmMakefile: Make FindTarget const.
ba276f2 cmMakefile: Make IsAlias const.
78c6af2 cmTarget: Make GetInterfaceLinkLibraries const.
284a234 cmTarget: Make GetTargetSourceFileFlags const.
757db44 cmTarget: Make custom command accessors API const.
0f87643 cmGeneratorTarget: Make GetIncludeDirectories const.
Merge topic 'use-generator-target' into next

f3e1ca9 Add a null check to the generator target accessor.
143fb14 Port some of the generator API to cmGeneratorTarget.
Merge topic 'remove-LOCATION-property-use' into next

a247911 Tests: Don't read the LOCATION property from build targets.
cffcdd8 KDevelop: Use GetLocation(0) instead of LOCATION property.