[FIR] Give external package fragments different module descriptors.

The inliner uses module descriptors to figure out if it needs to
regenerate objects.

We should avoid the use of descriptors in the inliner, but this
works as a first quick fix.

compiler/testData/codegen/box/annotations/instances/multimoduleInlining.kt

@@ -1,8 +1,3 @@
-// With FIR the annotation implementation class is not regenerated as it
-// is seen as coming from the same module.
-// See IrSourceCompilerForInline.kt:isCallInsideSameModuleAsCallee.
-// IGNORE_BACKEND_FIR: JVM_IR
-// FIR status: assertion failed: assert(one.javaClass.getEnclosingClass().getName() == "test.C")
 // TARGET_BACKEND: JVM_IR
 // IGNORE_DEXING
 // WITH_STDLIB