While collecting usage requirements from the `INTERFACE_*` properties of
directly linked targets, we internally generate `TARGET_PROPERTY:` and
`TARGET_OBJECTS:` generator expressions to refer to those properties on
those targets.  At the point we generate these expressions we already
have a pointer to an exact `cmGeneratorTarget` instance.

Switch from using the target name in these generator expressions to
using an internal unique name generated for each `cmGeneratorTarget`
instance to be referenced.  This avoids depending on the user-facing
target name to find the same target we already have.