More advanced xhtml <gi::Control> cross-component references

[JessicaMulein]

Once everything is working again, we will be back to operating by manually placing entries in a hashbucket with a name like {id}.Text, as applicable to each control type, such as a label.

It should be possible to treat that expression more literally and either fetch the property/variable value or execute the function and get the result if it's a function and/or () is appended. A custom control might be referenced by <gi::Value key="{id}.Somefunc()" />