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.cpp b/services/surfaceflinger/DisplayDevice.cpp
index 5f73fbc..9f882f1 100644
--- a/services/surfaceflinger/DisplayDevice.cpp
+++ b/services/surfaceflinger/DisplayDevice.cpp
@@ -510,21 +510,21 @@
     mDesiredActiveModeChanged = false;
 }
 
-void DisplayDevice::adjustRefreshRate(Fps leaderDisplayRefreshRate) {
+void DisplayDevice::adjustRefreshRate(Fps pacesetterDisplayRefreshRate) {
     using fps_approx_ops::operator==;
     if (mRequestedRefreshRate == 0_Hz) {
         return;
     }
 
     using fps_approx_ops::operator>;
-    if (mRequestedRefreshRate > leaderDisplayRefreshRate) {
-        mAdjustedRefreshRate = leaderDisplayRefreshRate;
+    if (mRequestedRefreshRate > pacesetterDisplayRefreshRate) {
+        mAdjustedRefreshRate = pacesetterDisplayRefreshRate;
         return;
     }
 
     unsigned divisor = static_cast<unsigned>(
-            std::round(leaderDisplayRefreshRate.getValue() / mRequestedRefreshRate.getValue()));
-    mAdjustedRefreshRate = leaderDisplayRefreshRate / divisor;
+            std::round(pacesetterDisplayRefreshRate.getValue() / mRequestedRefreshRate.getValue()));
+    mAdjustedRefreshRate = pacesetterDisplayRefreshRate / divisor;
 }
 
 std::atomic<int32_t> DisplayDeviceState::sNextSequenceId(1);