[wip] Fix testing and replace git apply with custom TS code

[ds300]

This PR should make patch-package's test suite cross-platform.

• Build pure-ts patch application
• Make patch-packages' existing test suite pass with pure-ts patch apply code
• Thoroughly unit test pure-ts apply code
• Handle file modes
• Test file mode handling
• Handle file copy pragmas
• Be quite sure that the full git patch spec is implement and tested
• Go through all behaviour and make new tests for untested things
• Check it's all working on windows