Detangling target dependencies in rtc_base_approved.

The eventual goal is to allow PlatformThread to use
SequencedTaskChecker, but getting to that point will require
some more detangling.

Here are (roughly) the steps taken in this CL:
* Make constructormagic a separate target.
* Move atomicops and arraysize to separate targets
* Move platform_thread_types to a separate target
* Move criticalsection to a separate target
* Move thread_checker to separate target
* Make sequenced_task_checker not depend on base_approved
* Move ptr_util to a separate target
* Move scoped_ptr to ptr_util
* Make rtc_task_queue_api not depend on base_approved
* Make sequenced_task_checker depend on rtc_task_queue_api
* Move rtc::Event to its own target
* Move basictypes.h to constructormagic
* Move format_macros and stringize_macros into constructormagic
* Rename constructormagic target to... macromagic
* Move stringencode to stringutils
* New target for safe_conversions
* Move timeutils to a new target.
* Move logging to a new target.
* Move platform_thread to a new target.
* Make refcount a new target (refcount, refcountedobject, refcounter).
* Remove rtc_base_approved from deps of TQ
* Remove a circular dependency between event tracer and platform thread.

Further steps will probably be to factor TaskQueue::Current() to not
be a part of the TaskQueue class itself and have it declared+implemented
in a target that's lower level than TQ itself. SequencedTaskChecker can
then depend on that target and avoid the TQ dependency. Once we're there,
PlatformThread will be able to depend on SequencedTaskChecker.

Attempted but eventually removed from this CL:
* Make TQ a part of rtc_base_approved
* Remove direct dependencies on sequenced_task_checker.
* Profit.

A few include-what-you-use updates along the way.
Fix a few targets that were depending on rtc_task_queue_api

Change-Id: Iee79aa2e81d978444c51b3005db9df7dc12d92a9
Bug: webrtc:8957
Reviewed-on: https://webrtc-review.googlesource.com/58480
Commit-Queue: Tommi <[email protected]>
Reviewed-by: Karl Wiberg <[email protected]>
Reviewed-by: Mirko Bonadei <[email protected]>
Reviewed-by: Danil Chapovalov <[email protected]>
Cr-Commit-Position: refs/heads/master@{#22487}

logging/BUILD.gn

@@ -219,7 +219,7 @@ rtc_static_library("rtc_event_log_impl_base") {
     ":rtc_event_log_impl_output",
     "../rtc_base:checks",
     "../rtc_base:rtc_base_approved",
-    "../rtc_base:rtc_task_queue_api",
+    "../rtc_base:rtc_task_queue",
     "../rtc_base:safe_minmax",
     "../rtc_base:sequenced_task_checker",
   ]

media/BUILD.gn

@@ -69,7 +69,8 @@ rtc_static_library("rtc_media_base") {
   deps = [
     "../api:audio_options_api",
     "../rtc_base:checks",
-    "../rtc_base:rtc_task_queue_api",
+    "../rtc_base:rtc_base_approved",
+    "../rtc_base:rtc_task_queue",
     "../rtc_base:sanitizer",
     "../rtc_base:sequenced_task_checker",
     "../rtc_base:stringutils",
@@ -450,7 +451,7 @@ if (rtc_include_tests) {
       "../modules/video_coding:video_coding_utility",
       "../p2p:rtc_p2p",
       "../rtc_base:checks",
-      "../rtc_base:rtc_task_queue_api",
+      "../rtc_base:rtc_task_queue",
       "../rtc_base:stringutils",
     ]
     sources = [
@@ -552,7 +553,7 @@ if (rtc_include_tests) {
       "../pc:rtc_pc",
       "../pc:rtc_pc_base",
       "../rtc_base:checks",
-      "../rtc_base:rtc_task_queue_api",
+      "../rtc_base:rtc_task_queue",
       "../rtc_base:stringutils",
       "../test:field_trial",
     ]

pc/BUILD.gn

@@ -382,7 +382,7 @@ if (rtc_include_tests) {
       "../rtc_base:rtc_base",
       "../rtc_base:rtc_base_approved",
       "../rtc_base:rtc_base_tests_utils",
-      "../rtc_base:rtc_task_queue_api",
+      "../rtc_base:rtc_task_queue",
       "../test:test_support",
     ]
 
@@ -516,7 +516,7 @@ if (rtc_include_tests) {
       "../rtc_base:rtc_base_approved",
       "../rtc_base:rtc_base_tests_main",
       "../rtc_base:rtc_base_tests_utils",
-      "../rtc_base:rtc_task_queue_api",
+      "../rtc_base:rtc_task_queue",
       "../system_wrappers:metrics_default",
       "../system_wrappers:runtime_enabled_features_default",
       "../test:audio_codec_mocks",