[SymbolGraphGen] only include the given symbol for qualified imports (#59852)

* only include the given symbol for qualified imports

rdar://96309088

* re-exporting one type should not allow unrelated types to sneak in

* ensure that children of re-exported types are also re-exported

test/SymbolGraph/Module/QualifiedImportWithExtensions.swift

@@ -0,0 +1,31 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend %S/Inputs/QualifiedImportWithExtensions/A.swift -module-name A -emit-module -emit-module-path %t/A.swiftmodule
+// RUN: %target-swift-frontend %s -module-name QualifiedImportWithExtensions -emit-module -emit-module-path /dev/null -I %t -emit-symbol-graph -emit-symbol-graph-dir %t/
+// RUN: %FileCheck %s --input-file %t/QualifiedImportWithExtensions.symbols.json
+// RUN: %FileCheck %s --input-file %t/QualifiedImportWithExtensions@A.symbols.json --check-prefix EXT
+
+@_exported import struct A.StructOne
+import A
+
+// An extension to a type that's been re-exported with a qualified import should appear in the
+// main symbol graph.
+extension A.StructOne {
+    public struct ExtendedStruct {}
+}
+
+// An extension to a type that's _not_ been re-exported should still appear in the extension symbol
+// graph, even if a different type from that module has been re-exported.
+extension A.StructTwo {
+    public struct InnerStruct {}
+}
+
+// Make sure that the `ExtendedStruct` type is present, and also that `StructOne`'s initializer is
+// present as well. The `InnerStruct` type should not be present since it's extending a type
+// that's not being re-exported.
+
+// CHECK-NOT: InnerStruct
+// CHECK-DAG: ExtendedStruct
+// CHECK-DAG: "precise":"s:1A9StructOneVACycfc"
+
+// EXT: InnerStruct
+// EXT-NOT: ExtendedStruct