Auto merge of #16303 - froydnj:rayon-version-bump, r=jdm

bump required rayon version to 0.7

...and bring jpeg-decoder along for the ride.  Minor tweaks were necessary because of rayon API changes.

- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors

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servo-tidy.toml

@@ -20,6 +20,7 @@ rand = [
   "parking_lot_core",
   "phf_generator",
   "rayon",
+  "rayon-core",
   "servo_rand",
   "servo-websocket",
   "tempdir",