feat(cmake): add ixm_property command to the public runtime

[bruxisma]

This introduces ixm_property, a command that was originally implemented as ixm_target_property in #21. However, as that PR is broken apart and into separate pieces I've been re-evaluating how each component should be named or how it works. Not much has changed with this command's implementation however it's name required an update as only target properties can be used with this command anyhow. There are possibly more useful additions that can be added for the final generator expression that is generated, however I'm keeping it as simple as it can be for now given its use-cases.