Rename "leader" display to "pacesetter"

"Leader" became ambiguous once we began to consider that there are two
orthogonal concepts that "leader" seems to imply:
- The display with the highest refresh rate (originally called "leader")
- The display that is refreshed first in a given update (assuming it's
  being updated)

To better distinguish between the two, we've come up with new names:
- pacesetter
- front runner (for the second concept)

Change uses of "leader" to "pacesetter" throughout SF and Scheduler.

Bug: 255635821
Bug: 256196556
Test: m
Change-Id: Ia02c35dd442d310695f1ce873fbaf30910c12419
diff --git a/services/surfaceflinger/DisplayDevice.h b/services/surfaceflinger/DisplayDevice.h
index b86d9be..29bbad5 100644
--- a/services/surfaceflinger/DisplayDevice.h
+++ b/services/surfaceflinger/DisplayDevice.h
@@ -247,9 +247,9 @@
 
     Fps getAdjustedRefreshRate() const { return mAdjustedRefreshRate; }
 
-    // Round the requested refresh rate to match a divisor of the leader
+    // Round the requested refresh rate to match a divisor of the pacesetter
     // display's refresh rate. Only supported for virtual displays.
-    void adjustRefreshRate(Fps leaderDisplayRefreshRate);
+    void adjustRefreshRate(Fps pacesetterDisplayRefreshRate);
 
     // release HWC resources (if any) for removable displays
     void disconnect();
@@ -290,7 +290,7 @@
     // for virtual displays to match this requested refresh rate.
     const Fps mRequestedRefreshRate;
 
-    // Adjusted refresh rate, rounded to match a divisor of the leader
+    // Adjusted refresh rate, rounded to match a divisor of the pacesetter
     // display's refresh rate. Only supported for virtual displays.
     Fps mAdjustedRefreshRate = 0_Hz;