[gardening] Migrate most files to be implicit-bool-conversion free

Issue https://dart-review.googlesource.com/c/sdk/+/115701

Change-Id: Ib579f0bbc8d694aec74afd837217316a10baf910
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/115707
Commit-Queue: Martin Kustermann <kustermann@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Daco Harkes <dacoharkes@google.com>

runtime/vm/compiler/assembler/disassembler_kbc.cc

@@ -315,7 +315,7 @@ void KernelBytecodeDisassembler::DecodeInstruction(char* hex_buffer,
                      hex_size - (i * kCharactersPerByte), " %02x", instr[i]);
     }
   }
-  if (out_instr_size) {
+  if (out_instr_size != nullptr) {
     *out_instr_size = instr_size;
   }