build: restore libplatform headers in distribution

Headers considered non-essential were removed in #37570, however the
libplatform API is actualy needed (and used) by external software
initiaing the v8 engine, see for example:
https://chromium.googlesource.com/v8/v8/+/refs/heads/main/samples/hello-world.cc

PR-URL: #39288
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Michael Dawson <midawson@redhat.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

tools/install.py

@@ -160,6 +160,9 @@ def headers(action):
   def wanted_v8_headers(files_arg, dest):
     v8_headers = [
       'deps/v8/include/cppgc/common.h',
+      'deps/v8/include/libplatform/libplatform.h',
+      'deps/v8/include/libplatform/libplatform-export.h',
+      'deps/v8/include/libplatform/v8-tracing.h',
       'deps/v8/include/v8.h',
       'deps/v8/include/v8-internal.h',
       'deps/v8/include/v8-platform.h',