Don't release XHR object until request complete

We previously figured that we could release the XHR object as soon as the JS
reference was out of scope. But the callbacks could still exist and thus the
XHR request should proceed.

This commit ensures the XHR instance remains valid so long as we have an active
request.

Might help with https://github.com/lightpanda-io/browser/issues/1448 but I can't
reliably reproduce this, so I'm not 100% sure it resolve the issue. That bug
appears to be caused by some timing interaction between the underlying HTTP
request and the v8 GC.

src/browser/webapi/net/XMLHttpRequest.zig

@@ -213,6 +213,8 @@ pub fn send(self: *XMLHttpRequest, body_: ?[]const u8) !void {
         .done_callback = httpDoneCallback,
         .error_callback = httpErrorCallback,
     });
+
+    page.js.strongRef(self);
 }
 pub fn getReadyState(self: *const XMLHttpRequest) u32 {
     return @intFromEnum(self._ready_state);
@@ -427,6 +429,8 @@ fn httpDoneCallback(ctx: *anyopaque) !void {
         .total = loaded,
         .loaded = loaded,
     }, local, page);
+
+    page.js.weakRef(self);
 }
 
 fn httpErrorCallback(ctx: *anyopaque, err: anyerror) void {
@@ -434,6 +438,7 @@ fn httpErrorCallback(ctx: *anyopaque, err: anyerror) void {
     // http client will close it after an error, it isn't safe to keep around
     self._transfer = null;
     self.handleError(err);
+    self._page.js.weakRef(self);
 }
 
 pub fn abort(self: *XMLHttpRequest) void {
@@ -442,6 +447,7 @@ pub fn abort(self: *XMLHttpRequest) void {
         transfer.abort(error.Abort);
         self._transfer = null;
     }
+    self._page.js.weakRef(self);
 }
 
 fn handleError(self: *XMLHttpRequest, err: anyerror) void {