wasm: add preload config for shared libraries build

Preload Qt plugins and QML imports by default. The json
files contain file listings generated by scripts in
qtbase/util/wasm/preload.

Pick-to: 6.6
Task-number: QTBUG-63925
Change-Id: I123b7a46fa19fa75ef214e8edb92e15ef635e5ba
Reviewed-by: Lorn Potter <lorn.potter@gmail.com>

src/corelib/Qt6WasmMacros.cmake

@@ -25,6 +25,14 @@ function(_qt_internal_wasm_add_target_helpers target)
         _qt_internal_wasm_export_name_for_target(_export_name ${target})
         set(APPEXPORTNAME ${_export_name})
 
+        # Shared library builds preload plugins and qml imports by default.
+        # The json files are generated by scripts in qtbase/util/wasm/preload
+        if (QT_FEATURE_shared)
+            set(PRELOAD "preload: ['qt_plugins.json', 'qt_qml_imports.json'],")
+        else()
+            set(PRELOAD "")
+        endif()
+
         get_target_property(target_output_directory ${target} RUNTIME_OUTPUT_DIRECTORY)
 
         get_target_property(is_test ${target} _qt_is_test_executable)

src/plugins/platforms/wasm/wasm_shell.html

@@ -59,6 +59,7 @@
                         },
                         entryFunction: window.@APPEXPORTNAME@,
                         containerElements: [screen],
+                        @PRELOAD@
                     }
                 });
             } catch (e) {