docs(guide/controller): change "hides" to "shadows"

"Shadows" should better convey the meaning of "overwriting the value of the property in the child
scope, while leaving the parent scope intact".
"Hides" could give the impression that it makes the property unavailable in the child scope and
leaving "overrides" only, could give the impression that the parent scope would be affected too,
especially to people not familiar with JavaScript's prototypal inheritance.

Closes #15375