AudioCodingModuleTest.TestAllCodecs: Create audio encoders the new way

Specifically, don't expect the ACM to be able to create encoders; we
have to give it an encoder that we make ourselves.

To make it work, I had to add support for the "ptime" parameter to the
L16 codec.

Bug: webrtc:8396
Change-Id: I3869422882611d2eed65d6c849ea7cd3ad6bd126
Reviewed-on: https://webrtc-review.googlesource.com/87423
Reviewed-by: Oskar Sundbom <ossu@webrtc.org>
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24217}
diff --git a/modules/audio_coding/BUILD.gn b/modules/audio_coding/BUILD.gn
index 8cda506..380f1bc 100644
--- a/modules/audio_coding/BUILD.gn
+++ b/modules/audio_coding/BUILD.gn
@@ -1327,6 +1327,7 @@
       "../..:webrtc_common",
       "../../api/audio:audio_frame_api",
       "../../api/audio_codecs:builtin_audio_decoder_factory",
+      "../../api/audio_codecs:builtin_audio_encoder_factory",
       "../../rtc_base:checks",
       "../../rtc_base:rtc_base_approved",
       "../../rtc_base/synchronization:rw_lock_wrapper",