[klib] Don't pass around metadata serialization closure

Pass the metadata serializer instance instead. This allows to further
reduce code duplication by introducing the common interface
`KlibSingleFileMetadataSerializer` for abstracting away K1 and K2
representation of a source file, as well as reusing
`Fir2KlibMetadataSerializer` across different backends.

KT-64392

wasm/wasm.tests/test/org/jetbrains/kotlin/wasm/test/converters/FirWasmKlibBackendFacade.kt

@@ -61,7 +61,7 @@ class FirWasmKlibBackendFacade(
                 configuration[CommonConfigurationKeys.MODULE_NAME]!!,
                 configuration,
                 inputArtifact.diagnosticReporter,
-                inputArtifact.sourceFiles,
+                inputArtifact.metadataSerializer,
                 klibPath = outputFile,
                 libraries.map { it.library },
                 inputArtifact.irModuleFragment,
@@ -71,9 +71,7 @@ class FirWasmKlibBackendFacade(
                 containsErrorCode = inputArtifact.hasErrors,
                 abiVersion = KotlinAbiVersion.CURRENT, // TODO get from test file data
                 jsOutputName = null
-            ) {
-                inputArtifact.serializeSingleFile(it)
-            }
+            )
         }
 
         // TODO: consider avoiding repeated libraries resolution