Rename ViEEncoder to VideoStreamEncoder

This CL:
- Renames the ViEEncoder class to VideoStreamEncoder, according to discussions.
- Renames variables 'vie_encode' to 'video_stream_encoder'.
- Formatting to match style guide.
- No other changes.

BUG=webrtc:8064

Review-Url: https://codereview.webrtc.org/2995433002
Cr-Commit-Position: refs/heads/master@{#19237}

webrtc/call/call_perf_tests.cc

diff --git a/webrtc/call/call_perf_tests.cc b/webrtc/call/call_perf_tests.cc
index f8461bf..558b75c 100644
--- a/webrtc/call/call_perf_tests.cc
+++ b/webrtc/call/call_perf_tests.cc
@@ -499,8 +499,8 @@
       switch (test_phase_) {
         case TestPhase::kStart:
           if (wants.max_pixel_count < std::numeric_limits<int>::max()) {
-            // On adapting down, ViEEncoder::VideoSourceProxy will set only the
-            // max pixel count, leaving the target unset.
+            // On adapting down, VideoStreamEncoder::VideoSourceProxy will set
+            // only the max pixel count, leaving the target unset.
             test_phase_ = TestPhase::kAdaptedDown;
           } else {
             ADD_FAILURE() << "Got unexpected adaptation request, max res = "