Improve formatting of config binder generator output

[layomia]

Intitial PR: #82179

From @eerhardt:

We are inconsistent on prefixing types with global::.

It would be better if we followed the same pattern in Regex and the RequestDelegateGenerator to put all the generated logic in a namesapce, with using statements inside the namespace declaration, and a file class implementation. That allows us to generate code that looks like how a user will write it.

See dotnet/aspnetcore#46180 (comment) and the 2nd bullet of #66432.

From @eiriktsarpalis: #82179 (comment)

Other comments:

#82179 (comment) (will address as part of #83531)
#82179 (comment)
#82179 (comment)

Tagging subscribers to this area: @dotnet/area-extensions-configuration
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Intitial PR: #82179

From @eerhardt:

We are inconsistent on prefixing types with global::.

It would be better if we followed the same pattern in Regex and the RequestDelegateGenerator to put all the generated logic in a namesapce, with using statements inside the namespace declaration, and a file class implementation. That allows us to generate code that looks like how a user will write it.

See dotnet/aspnetcore#46180 (comment) and the 2nd bullet of #66432.

From @eiriktsarpalis: #82179 (comment)

Other comments:

#82179 (comment)
#82179 (comment)
#82179 (comment)

Author:	layomia
Assignees:	layomia
Labels:	area-Extensions-Configuration, source-generator
Milestone:	8.0.0