URLSearchParam constructor support for object initialization

This adds support for:

```
new URLSearchParams({over: 9000});
```

The spec says that any thing that produces/iterates a sequence of string pairs
is valid. By using the lower-level JsObject, this hopefully takes care of the
most common cases. But I don't think it's complete, and I don't think we
currently capture enough data to make this work. There's no way for the JS
runtime to know if a value (say, a netsurf instance, or even a Zig instance)
provides an string=>string iterator.

src/browser/key_value.zig

@@ -102,6 +102,13 @@ pub const List = struct {
         });
     }
 
+    pub fn appendOwnedAssumeCapacity(self: *List, key: []const u8, value: []const u8) void {
+        self.entries.appendAssumeCapacity(.{
+            .key = key,
+            .value = value,
+        });
+    }
+
     pub fn delete(self: *List, key: []const u8) void {
         var i: usize = 0;
         while (i < self.entries.items.len) {

src/browser/url/url.zig

@@ -20,6 +20,7 @@ const std = @import("std");
 const Allocator = std.mem.Allocator;
 
 const parser = @import("../netsurf.zig");
+const Env = @import("../env.zig").Env;
 const Page = @import("../page.zig").Page;
 const FormData = @import("../xhr/form_data.zig").FormData;
 const HTMLElement = @import("../html/elements.zig").HTMLElement;
@@ -247,12 +248,31 @@ pub const URLSearchParams = struct {
     const URLSearchParamsOpts = union(enum) {
         qs: []const u8,
         form_data: *const FormData,
+        js_obj: Env.JsObject,
     };
     pub fn constructor(opts_: ?URLSearchParamsOpts, page: *Page) !URLSearchParams {
         const opts = opts_ orelse return .{ .entries = .{} };
         return switch (opts) {
             .qs => |qs| init(page.arena, qs),
             .form_data => |fd| .{ .entries = try fd.entries.clone(page.arena) },
+            .js_obj => |js_obj| {
+                const arena = page.arena;
+                var it = js_obj.nameIterator();
+
+                var entries: kv.List = .{};
+                try entries.ensureTotalCapacity(arena, it.count);
+
+                while (try it.next()) |js_name| {
+                    const name = try js_name.toString(arena);
+                    const js_val = try js_obj.get(name);
+                    entries.appendOwnedAssumeCapacity(
+                        name,
+                        try js_val.toString(arena),
+                    );
+                }
+
+                return .{ .entries = entries };
+            },
         };
     }
 
@@ -613,5 +633,9 @@ test "Browser.URLSearchParams" {
         .{ "ups.getAll('b')", "3" },
         .{ "fd.delete('a')", null }, // the two aren't linked, it created a copy
         .{ "ups.size", "3" },
+        .{ "ups = new URLSearchParams({over: 9000, spice: 'flow'})", null },
+        .{ "ups.size", "2" },
+        .{ "ups.getAll('over')", "9000" },
+        .{ "ups.getAll('spice')", "flow" },
     }, .{});
 }

src/runtime/js.zig

@@ -1366,6 +1366,13 @@ pub fn Env(comptime State: type, comptime WebApis: type) type {
                 }
             }
 
+            pub fn get(self: JsObject, key: []const u8) !Value {
+                const scope = self.scope;
+                const js_key = v8.String.initUtf8(scope.isolate, key);
+                const js_val = try self.js_obj.getValue(scope.context, js_key);
+                return scope.createValue(js_val);
+            }
+
             pub fn isTruthy(self: JsObject) bool {
                 const js_value = self.js_obj.toValue();
                 return js_value.toBool(self.scope.isolate);
@@ -1421,6 +1428,20 @@ pub fn Env(comptime State: type, comptime WebApis: type) type {
             pub fn isNullOrUndefined(self: JsObject) bool {
                 return self.js_obj.toValue().isNullOrUndefined();
             }
+
+            pub fn nameIterator(self: JsObject) ValueIterator {
+                const scope = self.scope;
+                const js_obj = self.js_obj;
+
+                const array = js_obj.getPropertyNames(scope.context);
+                const count = array.length();
+
+                return .{
+                    .count = count,
+                    .scope = scope,
+                    .js_obj = array.castTo(v8.Object),
+                };
+            }
         };
 
         // This only exists so that we know whether a function wants the opaque
@@ -1626,6 +1647,25 @@ pub fn Env(comptime State: type, comptime WebApis: type) type {
             }
         };
 
+        pub const ValueIterator = struct {
+            count: u32,
+            idx: u32 = 0,
+            js_obj: v8.Object,
+            scope: *const Scope,
+
+            pub fn next(self: *ValueIterator) !?Value {
+                const idx = self.idx;
+                if (idx == self.count) {
+                    return null;
+                }
+                self.idx += 1;
+
+                const scope = self.scope;
+                const js_val = try self.js_obj.getAtIndex(scope.context, idx);
+                return scope.createValue(js_val);
+            }
+        };
+
         fn compileModule(isolate: v8.Isolate, src: []const u8, name: []const u8) !v8.Module {
             // compile
             const script_name = v8.String.initUtf8(isolate, name);