Adjust some id bit shifts to fit inside 32 bit integers

Summary:
The DAP on vscode uses a JavaScript `number` for identifiers while the
Visual Studio version uses a C# `Int` for identifiers. lldb-vscode is
bit shifting identifiers 32 bits and then bitwise ORing another 32 bit
identifier into a 64 bit id to form a unique ID. Change this to
a a partitioning of the 32 bits that makes sense for the data types.

Reviewers: clayborg

Differential Revision: https://reviews.llvm.org/D53599

llvm-svn: 346346