[release/8.0] Fix binder gen compile issues due to inaccessible members and identifier name clashes

[github-actions]

Backport of #91657 to release/8.0

/cc @layomia

Customer Impact

Fixes two reported bugs. We expect users to hit them:

1. Compilation failures when private nested types are specified as config targets:

usingMicrosoft.Extensions.Configuration;internalclassProgram{privatestaticvoidMain(){}privatestaticCFoo(IConfigurationconfiguration){Cc=new();configuration.Bind(c);// Causes compile error.returnc;}privatesealedclassC{publicintValue{get;set;}}}

2. Errors due to generator using duplicate binding helper names to handle different types:

usingMicrosoft.Extensions.Configuration;IConfigurationconfiguration=newConfigurationBuilder().Build();// Generator emits identifier `Cint` to handle both types causing a name clash.varc1=newCint();varc2=newC<int>();configuration.Bind(c1);configuration.Bind(c2);internalclassC<T>{publicintValue{get;set;}}internalclassCint{publicintValue{get;set;}}

Testing

Extensive unit and emitted source regression tests were added to verify the fix.

Risk

Low. Contained fix for off-by-default component. Minimal custom identifier mangling is done, instead we use more reliable Roslyn APIs.

[ghost]

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

Issue Details

---

Backport of #91657 to release/8.0

/cc @layomia

Customer Impact

Testing

Risk

IMPORTANT: If this backport is for a servicing release, please verify that:

• The PR target branch is release/X.0-staging, not release/X.0.

• If the change touches code that ships in a NuGet package, you have added the necessary package authoring and gotten it explicitly reviewed.

Author:	github-actions[bot]
Assignees:	-
Labels:	area-Extensions-Configuration
Milestone:	-

[layomia]

I've addressed all feedback on #91974. cc @eiriktsarpalis.

[ericstj]

Approve this change for RC2. Thank you for minimizing your diff on these fixes and reusing the code from Json. @artl93 this one is ready for your review.

[artl93]

M2 approved.