Reorder Q050 before all other versions in server Alt-Svc

In order for us to deploy h3-29 in Chrome without 0-RTT support, we'll want to have Chrome support both h3-29 and h3-Q050 and then have our servers prefer Q050 (Chrome follows the server's preference). This CL solves the server part of this.

All tests in this change are from cl/327732758.

Reorder QUIC alt-svc, protected by gfe2_reloadable_flag_quic_preferred_altsvc_version

PiperOrigin-RevId: 328245609
Change-Id: I7136fd131acd6a73ca7d2c26d3a1ed155adf076e

quic/core/quic_version_manager.h

diff --git a/quic/core/quic_version_manager.h b/quic/core/quic_version_manager.h
index cbf5de1..8c277d7 100644
--- a/quic/core/quic_version_manager.h
+++ b/quic/core/quic_version_manager.h
@@ -50,6 +50,8 @@
   // Should be called in constructor and RefilterSupportedVersions.
   void AddCustomAlpn(const std::string& alpn);
 
+  bool disable_version_q050() const { return disable_version_q050_; }
+
  private:
   // Cached value of reloadable flags.
   // quic_disable_version_draft_29 flag