mbedTLS: Update to mbedTLS 3.6.4

mbedTLS 2.28 is now EOL, and will no longer receive security updates.

This commit backports from Godot 4 the changes needed to update to
mbedTLS 3.6 (new LTS), including TLSv1.3 support.

(cherry picked from commit 0770c9a4a3)

modules/mbedtls/crypto_mbedtls.h

@@ -46,6 +46,8 @@ private:
 	int locks = 0;
 	bool public_only = true;
 
+	int _parse_key(const uint8_t *p_buf, int p_size);
+
 public:
 	static CryptoKey *create();
 	static void make_default() { CryptoKey::_create = create; }