Add host target for perfetto protos on Android host builds

This CL introduces a "perfetto_trace_protos" static_library
target that allows to link the perfetto protobuf code on
host executable builds.
This CL also disentangles some awkward dep between proto:lite
targets and the IPC proto targets, that was indirectly causing
the core tracing target to depend on ipc.
Also fixes a small breakage on mac by removing an unnecessary
include in trace_to_text.

Sample usage:

In the .bp file:
---
cc_binary_host {
  name: "perfetto_proto_test",
  static_libs: [
    "perfetto_trace_protos",
    "libprotobuf-cpp-lite",
  ],
  srcs: [
    "host_test.cc"
  ],
}
---

Where host_test.cc:
---
#include "perfetto/trace/trace.pb.h"

int main(int, char** argv) {
  perfetto::protos::Trace trace;
  return trace.ParseFromString(std::string(argv[1]));
}
---

Bug: 73611302
Change-Id: Ie371e82941890a3a7567c30261befd756147cc1c
Test: manual. Checked that builds on mac.
diff --git a/BUILD.gn b/BUILD.gn
index 74e972e..ea02315 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -161,6 +161,15 @@
       ]
     }
   }
+
+  # This target exports perfetto trace protos in the Android build system,
+  # allowing both host and device targets to implement custom parsers based on
+  # our protos.
+  static_library("perfetto_trace_protos") {
+    deps = [
+      "protos/perfetto/trace:lite",
+    ]
+  }
 } else {
   group("lib") {
     public_configs = [ "gn:public_config" ]