Support conditional expressions in API1000/API1001 analyzers

[luissena]

Summary

Fixes #33105

The API convention analyzers (API1000 and API1001) did not inspect conditional (ternary) expressions, causing undocumented status codes to go undetected in return statements like:

return id == 0 ? NotFound() : Ok(new object());

While if/else and switch expressions were already handled, conditional expressions were silently skipped.

Changes

• Extended InspectReturnOperation in ActualApiResponseMetadataFactory to recurse into both branches (WhenTrue/WhenFalse) of IConditionalOperation, following the same pattern already used for ISwitchExpressionOperation
• Generalized the ISwitchExpressionArmOperation? parameter to IOperation? so both switch arm values and conditional branch values flow through the same code path
• Updated the existing test that documented this gap (NoDiagnosticsAreReturned_ForApiController_IfStatusCodesCannotBeInferred) — now that conditionals are inspected, the analyzer correctly reports undocumented status codes
• Added unit tests for conditional and nested conditional expressions
• Added integration tests for conditional returns, nested conditionals, expression-bodied members, and the all-documented-codes no-diagnostic case

Test plan

• All 215 existing + new analyzer tests pass
• Conditional expressions (a ? b : c) correctly produce API1000 diagnostics for undocumented status codes
• Nested conditionals (a ? b : c ? d : e) correctly produce diagnostics for all branches
• Expression-bodied members with conditionals are handled
• No diagnostics when all conditional branch status codes are documented
• No regressions in existing if/else, switch, and switch expression test coverage

[dotnet-policy-service]

Thanks for your PR, @@luissena. Someone from the team will get assigned to your PR shortly and we'll get it reviewed.