[clang] Add a new annotation token: annot_repl_input_end

[clang] Add a new annotation token: annot_repl_input_end

This patch is the first part of the below RFC:
https://discourse.llvm.org/t/rfc-handle-execution-results-in-clang-repl/68493

It adds an annotation token which will replace the original EOF token
when we are in the incremental C++ mode. In addition, when we're
parsing an ExprStmt and there's a missing semicolon after the
expression, we set a marker in the annotation token and continue
parsing.

Eventually, we propogate this info in ParseTopLevelStmtDecl and are able
to mark this Decl as something we want to do value printing. Below is a
example:

clang-repl> int x = 42;
clang-repl> x
// `x` is a TopLevelStmtDecl and without a semicolon, we should set
// it's IsSemiMissing bit so we can do something interesting in
// ASTConsumer::HandleTopLevelDecl.

The idea about annotation toke is proposed by Richard Smith, thanks!

Signed-off-by: Jun Zhang <jun@junz.org>
Differential Revision: https://reviews.llvm.org/D148997