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 <[email protected]>

apps/solidcraft/src/main.rs

@@ -117,9 +117,15 @@ fn services(cc: &eframe::CreationContext<'_>) -> Services {
     let open_parent = parent.clone();
     let program_parent = parent.clone();
     Services {
-        pick_open: Some(Box::new(move || {
-            let future = open_parent
-                .clone()
+        pick_open: Some(Box::new(move |first: &[&str]| {
+            // The file type the command reads comes first, so the picker opens on it (#1801).
+            let mut dialog = open_parent.clone();
+            if !first.is_empty() {
+                let label = first.iter().map(|e| e.to_uppercase()).collect::<Vec<_>>().join(", ");
+                let both: Vec<String> = first.iter().flat_map(|e| [e.to_lowercase(), e.to_uppercase()]).collect();
+                dialog = dialog.add_filter(label, &both);
+            }
+            let future = dialog
                 .add_filter(
                     "Designs, CAD files and meshes",
                     &[