8.0.0: Standalone code, phase 1

This release is the first in a series of releases to make the XP compiler more universally useful: Compiled code now doesn't include generated XP meta information by default, and is thus less dependant on XP Core, see https://github.com/xp-framework/compiler/projects/4.

• Merged PR #129: Add augmentable emitter to create property type checks
  for PHP < 7.4
  (@thekid)
• Fixed private and protected readonly properties being accessible from
  any scope in PHP < 8.1
  (@thekid)
• Merged PR #127: Do not emit XP meta information by default. This is
  the first step towards generating code that runs without a dependency
  on XP core.
  (@thekid)