Add SVG demo (#140)

Author: sonnyp

src/SVG/image.svg

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+using Gtk 4.0;
+using Adw 1;
+
+Adw.StatusPage {
+  title: _("SVG");
+  description: _("Display vectorial images at arbitrary sizes");
+
+  Box {
+    halign: center;
+    orientation: vertical;
+
+    DrawingArea drawing_area {
+      width-request: 128;
+      height-request: 128;
+    }
+
+    LinkButton {
+      label: _("Librsvg documentation");
+      uri: "https://gnome.pages.gitlab.gnome.org/librsvg/Rsvg-2.0/index.html";
+    }
+  }
+}

src/SVG/main.blp

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+import Rsvg from "gi://Rsvg?version=2.0";
+
+const drawing_area = workbench.builder.get_object("drawing_area");
+const svg = workbench.resolve("image.svg");
+
+const handle = Rsvg.Handle.new_from_file(svg);
+
+const [, width, height] = handle.get_intrinsic_size_in_pixels();
+console.log("SVG intrisic size", { width, height });
+
+function draw(_self, cr, width, height) {
+  console.log("drawing SVG at", { width, height });
+  handle.render_document(cr, new Rsvg.Rectangle({ x: 0, y: 0, width, height }));
+  cr.$dispose();
+}
+drawing_area.set_draw_func(draw);

src/SVG/main.js

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+{
+  "category": "user_interface",
+  "description": "Display vectorial images at arbitrary sizes",
+  "panels": ["ui", "code", "preview"],
+  "autorun": true
+}