apprt/embedded: escape the initial input string

Fixes #10214

src/apprt/embedded.zig

@@ -542,13 +542,20 @@ pub const Surface = struct {
         // If we have an initial input then we set it.
         if (opts.initial_input) |c_input| {
             const alloc = config.arenaAlloc();
+
+            // We need to escape the string because the "raw" field
+            // expects a Zig string.
+            var buf: std.Io.Writer.Allocating = .init(alloc);
+            defer buf.deinit();
+            try std.zig.stringEscape(
+                std.mem.sliceTo(c_input, 0),
+                &buf.writer,
+            );
+
             config.input.list.clearRetainingCapacity();
             try config.input.list.append(
                 alloc,
-                .{ .raw = try alloc.dupeZ(u8, std.mem.sliceTo(
-                    c_input,
-                    0,
-                )) },
+                .{ .raw = try buf.toOwnedSliceSentinel(0) },
             );
         }