Blazor binding updates

[guardrex]

Fixes #19789

Internal Review Topic (links to section)

• The approaches now avoid writing to a component parameter and use a backing field instead.
• Using the getter/setter approach that Ryan showed seems to only work when the component writes to the param per his original example. For this PR, I have the method that calls the binding delegate (OnPasswordChanged) make the checks. If that's not right, let me know how to handle that scenario. 👂 Even if that is the right spot, is calling return Task.CompletedTask; the right thing for a validation failure there? 👂 It seems to work well.

cc: @mrlife