Misc. small cleanups.

* Better param names
* Avoid using negative values for (bogus) placeholder channel counts (mostly in tests).  Since channels will be changing to size_t, negative values will be illegal; it's sufficient to use 0 in these cases.
* Use arraysize()
* Use size_t for counting frames, samples, blocks, buffers, and bytes -- most of these are already size_t in most places, this just fixes some stragglers
* reinterpret_cast<int64_t>(void*) is not necessarily safe; use uintptr_t instead
* Remove unnecessary code, e.g. dead code, needlessly long/repetitive code, or function overrides that exactly match the base definition
* Fix indenting
* Use uint32_t for timestamps (matching how it's already a uint32_t in most places)
* Spelling
* RTC_CHECK_EQ(expected, actual)
* Rewrap
* Use .empty()
* Be more pedantic about matching int/int32_t/
* Remove pointless consts on input parameters to functions
* Add missing sanity checks

All this was found in the course of constructing https://codereview.webrtc.org/1316523002/ , and is being landed separately first.

BUG=none
TEST=none

Review URL: https://codereview.webrtc.org/1534193008

Cr-Commit-Position: refs/heads/master@{#11191}

webrtc/modules/audio_coding/codecs/isac/fix/test/isac_speed_test.cc

@@ -92,7 +92,7 @@ float IsacSpeedTest::DecodeABlock(const uint8_t* bit_stream,
   value = WebRtcIsacfix_Decode(ISACFIX_main_inst_, bit_stream, encoded_bytes,
                                out_data, &audio_type);
   clocks = clock() - clocks;
-  EXPECT_EQ(output_length_sample_, value);
+  EXPECT_EQ(output_length_sample_, static_cast<size_t>(value));
   return 1000.0 * clocks / CLOCKS_PER_SEC;
 }