[llvm-debuginfo-analyzer] (03/09) - Logical elements

llvm-debuginfo-analyzer is a command line tool that processes debug
info contained in a binary file and produces a debug information
format agnostic “Logical View”, which is a high-level semantic
representation of the debug info, independent of the low-level
format.

The code has been divided into the following patches:

1) Interval tree
2) Driver and documentation
3) Logical elements
4) Locations and ranges
5) Select elements
6) Warning and internal options
7) Compare elements
8) ELF Reader
9) CodeView Reader

Full details:
https://discourse.llvm.org/t/llvm-dev-rfc-llvm-dva-debug-information-visual-analyzer/62570

This patch:

Logical elements
- All basic functionality for the logical elements:
  LVScope, LVLine, LVSymbol, LVType.
- The logical reader:
  LVReader.h

Reviewed By: psamolysov, probinson

Differential Revision: https://reviews.llvm.org/D125778