Fix the xml doc issue when the parameter's actual name is not the same as their variable name

[ArcturusZhang]

Fixes #5565
Fixes #5567
Fixes #5568

The root cause of the issue here is:
the ParameterProvider has a Name property, but it is actually the name of its input parameter, not its actual name in the code which we will never know until we actually write them into the code (because of the scope stuff and name collisions)

Therefore, this PR added a scope version of WriteXmlDocs and allows the parameters to be declared in the xml doc.
For a method, the parameters first appear in the xml docs, and then the method signature, therefore allowing the xml doc part to declare the parameter actually makes sense - since our code writer could only go forwards, no backwards.
With this change, if there is xml doc, when the code writer writes the xml doc for a parameter, if the parameter has a "not declared" CodeWriterDeclaration, it will declare it with the current scope (which is basically the same scope of the method), and then when it writes the method signature, it will find those parameters have been declared and it will just use the name, therefore everything works fine.
If there is no xml doc, when the code writer writes the method signature, it will find those parameters are not declared yet, and declares them. This is the same logic before this change.

To achieve this, this PR has to change the start tag and end tag in the XmlDocProvider to be FormattableStrings. This allows us to utilize the ability of CodeWriter to automatically resolve the declaration of the parameter inside the tag.

[azure-sdk]

API change check

API changes are not detected in this pull request.

[JoshLove-msft]

The approach seems reasonable to me considering the alternative would need to involve either rewinding the writer and writing the xml docs after the method or otherwise some way of constructing scopes ahead of time before writing.