[ hackfmt ] Hackfmt fails to format modern xhp class declarations

[lexidor]

Describe the bug
Hackfmt fails to format files containing xhp class declarations.

Standalone code, or other way to reproduce the problem

Placed in file.hack

xhp class F {
            }

Steps to reproduce the behavior:

1. hackfmt file.hack

Expected behavior

Expected format output like this:

xhp class F {
}

Actual behavior

$ hackfmt file.hack
(1,5)-(1,5) Encountered unexpected token `XHP`.
File failed to parse without errors

Environment

• Operating system

'Ubuntu 18.04'

• Installation method

'apt-get with dl.hhvm.com repository'

• HHVM Version

Please include the output of hhvm --version and hh_client --version

HipHop VM 4.80.6 (rel)
Compiler: 1626798808_939072534
Repo schema: d1ae8e21bf3419a65f12a010527485564e719d07
hackc-80878ab52458a2db6bcc91cf1747df93ca647992-4.80.6

---

HipHop VM 4.102.7 (rel)
Compiler: 1647389495_389373763
Repo schema: d1ae8e21bf3419a65f12a010527485564e719d07
hackc-d09f6f5fa7d62773a2784453de10384260f720d7-4.102.7

---

HipHop VM 4.128.4 (rel) (non-lowptr)
Compiler: 1648578890_742766188
Repo schema: 3bffe303632e801137165e448a12a0707742584f
hackc-8b25016efed065c93522fd47cf375a24a364ab71-4.128.4

---

HipHop VM 4.164.0 (rel) (non-lowptr)
Compiler: 1657309234_951459400
Repo schema: c762591bd64e87a7b3be143e72e4a2e69ad9179f
hackc-34126416fe6f3d0ed29cbc7bc914e61c3c7607e4-4.164.0