Use the PHPAST linter in Phorge

Summary:
Add the PHPAST linter in Phorge, to support newer PHP syntax.

Requires that D26516 be applied to rARC locally.

Test Plan:
* Run `arc patch D26516` on `arcanist/`
* Run `arc lint --everything --never-apply-patches --severity disabled --output summary`

Reviewers: O1 Blessed Committers, avivey

Reviewed By: O1 Blessed Committers, avivey

Subscribers: avivey, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T16309

Differential Revision: https://we.phorge.it/D26517

.arclint

···
     "nolint": {
       "type": "nolint"
     },
+    "phpast": {
+      "type": "phpast",
+      "include": "(\\.php$)",
+      "standard": "phutil.phpast"
+    },
     "phutil-library": {
       "type": "phutil-library",
       "include": "(\\.php$)"