[OWNERS] futex-emulation owners += marja

The majority of the content is the Atomics.waitAsync implementation
which I wrote.

"git blame" shows I've touched 123 / 274 lines in futex-emulation.h and
551 / 875 lines in futex-emulation.cc.

(Status before https://chromium-review.googlesource.com/c/v8/v8/+/2319989 which was moving
code around.)

No-Try: True
Change-Id: Ib31dc0bb778aed90d5c4c56ccb0e556655ce6946
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2332813
Commit-Queue: Marja Hölttä <marja@chromium.org>
Reviewed-by: Mythri Alle <mythria@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69202}

src/execution/OWNERS

@@ -8,4 +8,6 @@ petermarshall@chromium.org
 szuend@chromium.org
 verwaest@chromium.org
 
+per-file futex-emulation.*=marja@chromium.org
+
 # COMPONENT: Blink>JavaScript>Runtime