[lld][InputGraph] Change the Resolver to use inputGraph

Changes :-

a) Functionality in InputGraph to insert Input elements at any position
b) Functionality in the Resolver to use nextFile
c) Move the functionality of assigning file ordinals to InputGraph
d) Changes all inputs to MemoryBuffers
e) Remove LinkerInput, InputFiles, ReaderArchive

llvm-svn: 192081
diff --git a/lld/lib/ReaderWriter/CoreLinkingContext.cpp b/lld/lib/ReaderWriter/CoreLinkingContext.cpp
index fdc56ec..bc9a009 100644
--- a/lld/lib/ReaderWriter/CoreLinkingContext.cpp
+++ b/lld/lib/ReaderWriter/CoreLinkingContext.cpp
@@ -272,6 +272,7 @@
 CoreLinkingContext::CoreLinkingContext() {}
 
 bool CoreLinkingContext::validateImpl(raw_ostream &diagnostics) {
+  _reader = createReaderYAML(*this);
   return true;
 }
 
@@ -288,13 +289,6 @@
   }
 }
 
-error_code CoreLinkingContext::parseFile(LinkerInput &input,
-    std::vector<std::unique_ptr<File>> &result) const {
-  if (!_reader)
-    _reader = createReaderYAML(*this);
-  return _reader->parseFile(input, result);
-}
-
 Writer &CoreLinkingContext::writer() const {
   if (!_writer)
     _writer = createWriterYAML(*this);