vagrant: Add parallels as a provider.

There are file sharing issues with the macOS 10.15.6 and
vagrant. var/remote_cache_prefix was an empty file when using
VirtualBox and Docker on macOS.
Using parallels as a provider for vagrant fixes the issue.

Use --watch-poll which makes webpack to recompile
automatically on file changes, since inotify is not
working here too.

Vagrantfile

@@ -120,6 +120,13 @@ Vagrant.configure(VAGRANTFILE_API_VERSION) do |config|
     vb.cpus = vm_num_cpus
   end
 
+  config.vm.provider "parallels" do |prl, override|
+	override.vm.box = "bento/ubuntu-18.04"
+	override.vm.box_version = "202005.21.0"
+	prl.memory = vm_memory
+	prl.cpus = vm_num_cpus
+  end
+
 $provision_script = <<SCRIPT
 set -x
 set -e

docs/development/setup-vagrant.md

@@ -85,7 +85,8 @@ Jump to:
 
 (For a non-free option, but better performance, you can also use [VMWare
 Fusion][vmware-fusion-dl] with the [VMWare Fusion Vagrant
-plugin][vagrant-vmware-fusion-dl].)
+plugin][vagrant-vmware-fusion-dl] or [Parallels Desktop][parallels-desktop-dl] as
+a provider for Vagrant.)
 
 Now you are ready for [Step 2: Get Zulip code](#step-2-get-zulip-code).
 
@@ -1026,6 +1027,7 @@ remove the `GUEST_CPUS` and `GUEST_MEMORY_MB` lines from
 [vbox-dl]: https://www.virtualbox.org/wiki/Downloads
 [vmware-fusion-dl]: https://www.vmware.com/products/fusion.html
 [vagrant-vmware-fusion-dl]: https://www.vagrantup.com/vmware/
+[parallels-desktop-dl]: https://www.parallels.com/products/desktop/
 [install-advanced]: ../development/setup-advanced.md
 [rtd-git-guide]: ../git/index.md
 [rtd-testing]: ../testing/testing.md

tools/webpack

@@ -53,7 +53,7 @@ def build_for_dev_server(host: str, port: str, minify: bool, disable_host_check:
         for line in mounts:
             fields = line.split()
             if fields[1] == cwd:
-                inotify_broken = fields[2] in ["nfs", "vboxsf"]
+                inotify_broken = fields[2] in ["nfs", "vboxsf", "prl_fs"]
     if inotify_broken:
         webpack_args.append('--watch-poll=1000')