protozero: rename protoc_plugin -> protozero_plugin (and ipc)

Non functional refactoring. Just changes the name of the
plugin executable and gets rid of the extra .h/.cc in the plugin
code. This keeps it consistent with the ipc plugin and allows to
disambiguate with the upcoming cpp stub generator.

Bug: 132880619
Change-Id: Ib940a8689353677d7c2c5e5f64880ea97c5290e0
diff --git a/BUILD.gn b/BUILD.gn
index 74ca6bb..eeb8f7d 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -46,7 +46,7 @@
   testonly = true  # allow to build also test targets
   deps = [
     ":perfetto_unittests",
-    "src/protozero/protoc_plugin($host_toolchain)",
+    "src/protozero/protoc_plugin:protozero_plugin($host_toolchain)",
   ]
   if (perfetto_build_standalone || perfetto_build_with_android ||
       build_with_chromium) {