Add GetRegistrationId extension to expose a registration's unique ID (#1327)

[tillig]

Summary

Fixes #1327. There was no way to obtain a stable, unique identity for a registration from the IRegistrationBuilder returned by RegisterType / Register / RegisterInstance. The identity already exists internally (SingleRegistrationStyle.Id, which flows to IComponentRegistration.Id), but it was not reachable from the builder, so callers could not (for example) use it as a key in ContainerBuilder.Properties to track per-registration state before the container is built.

Fix

Adds a single extension method:

public static Guid GetRegistrationId<TLimit, TActivatorData>(
    this IRegistrationBuilder<TLimit, TActivatorData, SingleRegistrationStyle> registration)

It returns registration.RegistrationStyle.Id — the same Guid that appears on IComponentRegistration.Id after the container is built.

The method is generically constrained to SingleRegistrationStyle, so it is only callable on single-component registrations. Multi-component registrations (open generics via RegisterGeneric, assembly scanning, adapters, decorators) use DynamicRegistrationStyle and have no single stable identity — calling GetRegistrationId on them is a compile-time error rather than a runtime throw.

No interface changes (avoids breaking external implementers of IRegistrationBuilder); purely additive API. Placed alongside the similarly-constrained PreserveExistingDefaults.

Tests

6 tests (all tagged #1327): the returned id matches IComponentRegistration.Id after build for RegisterType, Register(lambda), and RegisterInstance; the id is stable across repeated calls; distinct registrations get distinct ids; and the null-argument guard. No compile test for the dynamic-style case is possible (it's a compile error by design).

Verified: the Guid is assigned once at SingleRegistrationStyle construction and never reassigned, flowing unchanged into IComponentRegistration.Id via RegistrationBuilder.CreateRegistration. Full XML docs; zero warnings; Autofac.Test passes; format clean.

Versioning

Because this adds new public API (a backwards-compatible additive surface change), this PR bumps the version in default.proj from 9.1.1 to 9.2.0 per semver. The bug fixes already merged to develop since 9.1.1 (#1485, #1486, #1487, #1488, #1489) will ship together in the 9.2.0 release.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.93%. Comparing base (0e724c2) to head (40fe97d).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1490      +/-   ##
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- Coverage    78.00%   77.93%   -0.08%     
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  Files          217      217              
  Lines         5897     5900       +3     
  Branches      1265     1266       +1     
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- Hits          4600     4598       -2     
- Misses         759      764       +5     
  Partials       538      538              

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