wasm: preload_qml_imports.py: get dependencies from the dylink.0 section

The qtbase/util/wasm/preload/preload_qml_imports.py script calls qmlimportscanner to get a list of QML imports to preload. It then needs to determine the dependencies of each plugin in order to add those as well to the preload list.

This is currently implemented by scanning the plugin binaries for strings with the ".so" ending, see find_dependencies(). A better approach would be to parse the wasm modules and get dependencies in a structured way.

Emscripten stores this information in a custom section in the wasm binary named "dynlink.0" . We should be able to get to this section using a wasm parsing library (or implement a simple parser by hand since we only need one section), and then extract the dependencies.