[DebugInfo] generate btf_tag annotations for func parameters

Generate btf_tag annotations for function parameters.
A field "annotations" is introduced to DILocalVariable, and
annotations are represented as an DINodeArray, similar to
DIComposite elements. The following example illustrates how
annotations are encoded in IR:
    distinct !DILocalVariable(name: "info",, arg: 1, ..., annotations: !10)
    !10 = !{!11, !12}
    !11 = !{!"btf_tag", !"a"}
    !12 = !{!"btf_tag", !"b"}

Differential Revision: https://reviews.llvm.org/D106620

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -1994,6 +1994,7 @@ void ModuleBitcodeWriter::writeDILocalVariable(
   Record.push_back(N->getArg());
   Record.push_back(N->getFlags());
   Record.push_back(N->getAlignInBits());
+  Record.push_back(VE.getMetadataOrNullID(N->getAnnotations().get()));
 
   Stream.EmitRecord(bitc::METADATA_LOCAL_VAR, Record, Abbrev);
   Record.clear();