Generate bindings for C++ standard library

This cl implements a new bindings_for_toolchain_headers rule that generates bindings for the C++ standard library headers. The list of headers that we consider public is located under devtools/rust/cc_interop/rs_bindings_from_cc/BUILD. I'll expand it in a followup cl.

Currently the grte headers are considered to be non-public headers that are part of the C++ standard library. We'll create a separate target for them in a followup cl.

We will not be generating bindings for the clang builtin headers.

PiperOrigin-RevId: 426237240
diff --git a/rs_bindings_from_cc/importer.cc b/rs_bindings_from_cc/importer.cc
index 6275385..35af0f6 100644
--- a/rs_bindings_from_cc/importer.cc
+++ b/rs_bindings_from_cc/importer.cc
@@ -538,11 +538,7 @@
   // consider it a textual header. In that case we go up the include stack
   // until we find a header that has an owning target.
 
-  // TODO(b/208377928): We currently don't have a target for the headers in
-  // Clang's resource directory, so for the time being we return a fictional
-  // "//:virtual_clang_resource_dir_target" for system headers.
-  while (source_location.isValid() &&
-         !source_manager.isInSystemHeader(source_location)) {
+  while (source_location.isValid()) {
     if (source_location.isMacroID()) {
       source_location = source_manager.getExpansionLoc(source_location);
     }