[ORC] Add a LLJITWithThinLTOSummaries example in OrcV2Examples

The example demonstrates how to use a module summary index file produced for ThinLTO to:
* find the module that defines the main entry point
* find all extra modules that are required for the build

A LIT test runs the example as part of the LLVM test suite [1] and shows how to create a module summary index file.
The code also provides two Error types that can be useful when working with ThinLTO summaries.

[1] if LLVM_BUILD_EXAMPLES=ON and platform is not Windows

Differential Revision: https://reviews.llvm.org/D85974