Insert SVG: the file picker opens on SVG files (#1801) (#1827)

* claim: #1801

* Insert SVG: the file picker opens on SVG files (#1801)

Every Open went through one host picker whose filters start with designs, CAD
files and meshes, so Insert SVG (and Insert DXF) in a sketch opened on STEP,
IGES and meshes, and the SVG file had to be found under another filter.

The host's pick_open now takes the extensions the command reads and offers
them as the picker's first, default filter. Insert SVG and Insert DXF pass
their type; every other Open passes none and keeps the list it had. The
browser host ignores them (it shows its own file panel).

---------

Co-authored-by: MateuszSychXpl <151755914+MateuszSychXpl@users.noreply.github.com>

crates/ui-egui/src/params_dialog.rs

@@ -144,7 +144,7 @@ pub fn show(app: &mut SolveApp, ctx: &egui::Context) {
                 ui.add(egui::TextEdit::singleline(&mut d.filter).hint_text(crate::i18n::tr_label("Filter")).desired_width(180.0));
                 ui.separator();
                 if ui.button("Import…").on_hover_text(crate::i18n::tr_label("CSV or JSON: updates existing parameters, adds new ones")).clicked() {
-                    app.pick_open_command("parameters.import", json!({}));
+                    app.pick_open_command("parameters.import", json!({}), &[]);
                 }
                 for (label, ext) in [("Export CSV…", "csv"), ("Export JSON…", "json")] {
                     if ui.button(label).clicked() {