FMIL: Remove left-over functions `fmi2_xml_set_default_experiment_XXX`, for #3267
FMIL: Comment out tests that use `fmi2_xml_get_derivatives_list` etc. since this will be reimplemented in the context of the new `<ModelStructure>` tag for #3267
FMIL: Comment out `*_get_derivatives_list` functions etc. for #3267, since these will be reimplemented in the context of the new `<ModelStructure>` tag.
FMIL: Remove functions `*get_dependencies_*_on_*` for #3267, since the `<ModelStructure>` format has changed and will be presented differently to the user.
FMIL: Remove the old-format content of `<ModelStructure>` from all FMI2 test FMU XML files and remove the code that parses it, for #3267.

Also temporarily hard-code `fmi2_import_me_test.c` to 2 states, since `<ModelStructure>` was used to find the number of continuous states.
FMIL: Remove all of contents of `fmi2_xml_model_structure_t` except `isValidFlag` for #3267, since XML `<ModelStructure>` format has changed.

Also remove contents of function `fmi2_xml_check_model_structure`, which checked the old format.
Function `fmi2_xml_free_model_structure` can currently not get any callbacks and so cannot free the structure; this should be fixed as soon as the structure is filled with new contents.
FMIL: Remove functions `fmi2_import_get_derivative_index` etc, and the corresponding fields in `fmi2_xml_variable_t` for #3267, since they correspond to the old `<ModelStructure>` format.

Also update `fmi2_import_xml_test.cc` not to use these functions.
FMIL: Add `<Real>` attributes `derivative` and `reinit` for #3267: parsing, record in `fmi2_xml_variable_t`, add to `modelDescription_me.xml`.

Also clean up unused attribute names from previous form of `<ModelStructure>`.
FMIL: Update FMI2 test FMU XML files to get rid of a number of errors and warnings that ended up in the test log, for #3267.

Also comment out XML elements that were used under `<ModelStructure>` to avoid errors/warnings from empty `<ModelStructure>`.
FMIL: Add parsing of `<ScalarVariable>` attributes `<previous>` and `canHandleMultipleSetPerTimeInstant` for #3267.

Also add some comments and missing typecasts for previously add attributes.