[LLVM][IR] Add location tracking to LLVM IR parser (#155797)

This PR is part of the LLVM IR LSP server project
([RFC](https://discourse.llvm.org/t/rfc-ir-visualization-with-vs-code-extension-using-an-lsp-server/87773))

To be able to make a LSP server, it's crucial to have location
information about the LLVM objects (Functions, BasicBlocks and
Instructions).

This PR adds:
 * Position tracking to the Lexer
 * A new AsmParserContext class, to hold the new position info
 * Tests to check if the location is correct

The AsmParserContext can be passed as an optional parameter into the
parser. Which populates it and it can be then used by other tools, such
as the LSP server.

The AsmParserContext idea was borrowed from MLIR. As we didn't want to
store data no one else uses inside the objects themselves. But the
implementation is different, this class holds several maps of Functions,
BasicBlocks and Instructions, to map them to their location.

And some utility methods were added to get the positions of the
processed tokens.