List of improvements for incubating package `patch-rnmacos`

[kelset]

This issue wants to track a series of improvements that can be done for the draft package @rnx-kit/patch-rnmacos to get it to be is a better shape (and potentially graduate from draft into something that we'd like to share more broadly).

Here's the list:

• add proper testing. Currently, there is none.
• Some modules names are camelCase and some are snake_case. Make it consistent within the package (either one is fine).
• the tool currently defaults to Windows values: it should be able to figure out what platform it is on and choose an appropriate set of executables.
• change the --confirm true param into --write without a value.
• change program.version("0.0.1"); in cli.ts to pick up the version from the package.json's field version
• move the default inclusion and exclusion lists out of code and into a json or text file.
• in diffRepos.ts, the code between the onHit and onMiss callbacks is nearly identical. Lift it out and share
• remove commented out code if deemed useless
• replace packages/draft-patch-rnmacos/src/file_compare.ts with hasha.fromFileSync() (from https://github.com/sindresorhus/hasha). It does the same thing, it's maintained by someone else, and it uses worker threads for faster perf.
• make exclusion list be pre-processed to exclude ./ or .\ once, ahead of time. See for example ~L114 in packages/draft-patch-rnmacos/src/fs_utils.ts
• Git can generate and apply file-level patches. Why not use that, vs writing our own impl of parsing and applying patch files? (see patch/apply.ts as an example of something that could be replaced potentially)
• a few more improvements for patch/apply.ts:
  • change logic on L30 - from comment: "What about a check to see if the target exists? If it does, that seems like a problem.... by default, moveSync fails if the target exists already."
  • comment: The dryRun checks seem valuable in the non-dryrun case. Consider running them all the time, and then only doing the destructive ops when !dryRun.
  • L63 - from comment: "What about other mode changes, like read and write?"
• logic in L176->L197 for packages/draft-patch-rnmacos/src/diffRepos.ts should be revised: If something is present in both inclusionList as well as exclusionList, you should probably fail the whole run.
• add a new command update-patches, to attempt fixing a patch after the codebase has changed. See an attempt at implementation here: Add update-android-patches script react-native-macos#864

Feel free to pick up any one of these bullet points separately - simply leave a comment here to let everyone know that you are working on it.

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most of the items listed were originally reported here #1135

[afoxman]

• patch tool has a number of default app paths in it. these should be replaced with parameterized values.
• patch tool makes assumptions about running on Windows. it needs to handle cases where it is run on MacOS or Ubuntu (CI loops).