Reland "Mark all bool conversion operators as explicit"

This is a reland of 325789c4576b60147ee1ef225d438cbb740f65ff

Original change's description:
> Mark all bool conversion operators as explicit
>
> An explicit bool conversion operator will still be used implicitly
> when an expression appears in "bool context", e.g., as the condition
> in an if statement, or as argument to logical operators. The
> `explicit` annotation prevents conversion in other contexts, e.g.,
> converting both a and b to bool in an expression like `a == b`.
>
> Bug: None
> Change-Id: I79ef35b1ea831e6011ae472900375ae8a3e617ab
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/250664
> Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
> Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
> Commit-Queue: Niels Moller <nisse@webrtc.org>
> Cr-Commit-Position: refs/heads/main@{#35927}

Bug: None
Change-Id: Ie057dfc8c0b5c498e2c8daff7620172c89f0e011
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/251380
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#35962}

logging/rtc_event_log/events/rtc_event_field_encoding_parser.h

@@ -36,7 +36,9 @@ class RtcEventLogParseStatus {
   }
 
   bool ok() const { return error_.empty(); }
-  ABSL_DEPRECATED("Use ok() instead") operator bool() const { return ok(); }
+  ABSL_DEPRECATED("Use ok() instead") explicit operator bool() const {
+    return ok();
+  }
 
   std::string message() const { return error_; }
 

modules/congestion_controller/goog_cc/probe_controller.cc

@@ -225,7 +225,7 @@ std::vector<ProbeClusterConfig> ProbeController::OnMaxTotalAllocatedBitrate(
         probes.push_back(second_probe_rate.bps());
     }
     return InitiateProbing(at_time_ms, probes,
-                           config_.allocation_allow_further_probing);
+                           config_.allocation_allow_further_probing.Get());
   }
   max_total_allocated_bitrate_ = max_total_allocated_bitrate;
   return std::vector<ProbeClusterConfig>();

modules/desktop_capture/linux/wayland/shared_screencast_stream.cc

@@ -152,7 +152,7 @@ class ScopedBuf {
     }
   }
 
-  operator bool() { return map_ != MAP_FAILED; }
+  explicit operator bool() { return map_ != MAP_FAILED; }
 
   void initialize(uint8_t* map, int map_size, int fd) {
     map_ = map;

rtc_base/experiments/field_trial_parser.h

@@ -220,7 +220,7 @@ class FieldTrialFlag : public FieldTrialParameterInterface {
   explicit FieldTrialFlag(std::string key);
   FieldTrialFlag(std::string key, bool default_value);
   bool Get() const;
-  operator bool() const;
+  explicit operator bool() const;
 
  protected:
   bool Parse(absl::optional<std::string> str_value) override;

sdk/objc/unittests/scoped_cftyperef_tests.mm

@@ -16,7 +16,7 @@ namespace {
 struct TestType {
   TestType() : has_value(true) {}
   TestType(bool b) : has_value(b) {}
-  operator bool() { return has_value; }
+  explicit operator bool() { return has_value; }
   bool has_value;
   int retain_count = 0;
 };