[clang][ExtractAPI] Complete declaration fragments for TagDecl types defined in a typedef

enums and structs declared inside typedefs have incorrect declaration fragments, where the typedef keyword and other syntax is missing.

For the following struct:

typedef struct Test {
    int hello;
} Test;
The produced declaration is:

"declarationFragments": [
  {
    "kind": "keyword",
    "spelling": "struct"
  },
  {
    "kind": "text",
    "spelling": " "
  },
  {
    "kind": "identifier",
    "spelling": "Test"
  }
],
instead the declaration fragments should represent the following

typedef struct Test {
    …
} Test;

This patch removes the condition in SymbolGraphSerializer.cpp file and completes declaration fragments

Reviewed By: dang

Differential Revision: https://reviews.llvm.org/D146385