populate Response.statusText for network responses

Fetch responses from the network now have their statusText set using
the HTTP status phrase (e.g. "OK", "Not Found"), matching the Fetch
spec and the existing XMLHttpRequest behavior.

src/browser/webapi/net/Fetch.zig

@@ -117,6 +117,7 @@ fn httpHeaderDoneCallback(transfer: *Http.Transfer) !bool {
     }
 
     res._status = header.status;
+    res._status_text = std.http.Status.phrase(@enumFromInt(header.status)) orelse "";
     res._url = try arena.dupeZ(u8, std.mem.span(header.url));
     res._is_redirected = header.redirect_count > 0;
 

src/browser/webapi/net/Response.zig

@@ -95,10 +95,6 @@ pub fn getStatus(self: *const Response) u16 {
 }
 
 pub fn getStatusText(self: *const Response) []const u8 {
-    // @TODO
-    // This property is meant to actually capture the response status text, not
-    // just return the text representation of self._status. If we do,
-    // new Response(null, {status: 200}).statusText, we should get empty string.
     return self._status_text;
 }