**Data matters, please review**

This is a rework of #2891 #2890 and #2882 . This will also fix #2724 and fix #2900 , close #2779 

**Introduction**

I add a function called `unlink_persist_data($dir)`, which recursively unlink all junction/hard link in the given directory. This affects some sub-commands which have interaction with junction/hard link:

- `scoop-install`: the persisting logic has been improved as follow:
  1. if there are data in the `persist` folder, also in app(`source`) folder, rename that one located in app folder (e.g. app's default setting files) with a `original` suffix, then create link from `persist` to  app
  2. if there are data in the `persist` folder, but no in app(`source`) folder, just create link from `persist` to  app
  3. if there is no data in the `persist` folder (e.g. fresh install), but there are data in app(`source`) folder (e.g. app's default setting files), we will just use that default setting files as the first-time persisting. So move that files from app folder to `persist` folder, then create link from `persist` to  app
  4. But what if if there is neither data in the `persist` folder (e.g. fresh install), nor in the app(`source`) folder (e.g. setting files will be created after first startup, like `Everthing.db`). We need to create empty persisting target in the `persist` folder. But by default we can't know if a persisting target is a file or a directory (e.g. `conf.d`). So we create a directory by default, and to avoid this, manifest maintainers should use `pre_install` to manually create the source file before persisting.
- `scoop-reset`: `reset` command uses the logic of `install`, but there is a problem: before re-persisting data, there have been `junction/hard link` in the app(`source`) folder. It will throw an exception of file exists #2724 . To fix this, we should unlink all old link before re-persisting, using `unlink_persist_data`.
- `scoop-uninstall`: `Remove-Item` can not remove `NTFS junction`, we need to unlink all persistting data, before uninstalling/deleting an app, but keeping persisting data.
- `scoop-cleanup`: like `uninstall`, `Remove-Item` can not remove `NTFS junction`, we need to unlink all persistting data, before deleting old versions of an app. Before PR #2882 , it use `fsutil.exe` to unlink junction, which is not friendly to restricted users (#2832 and #2881 ).

Beyond the logic improvement, there is a new feature now: it supports sub-folder data persisting, like:

```json
{
    "homepage": "https://scoop.sh",
    "description": "A dummy manifest for scoop tests.",
    "license": "Freeware",
    "version": "1.1.0",
    "url": "https://get.scoop.sh",
    "pre_install": [
        "if (!(test-path \"$dir\\dummy.txt\")) { new-item -force \"$dir\\dummy.txt\" -itemtype file | out-null }",
        "if (!(test-path \"$dir\\dummydir\")) { new-item \"$dir\\dummydir\" -itemtype directory | out-null }",
        "if (!(test-path \"$dir\\subdir\")) { new-item \"$dir\\subdir\" -itemtype directory | out-null }",
        "if (!(test-path \"$dir\\subdir\\subdummydir\")) { new-item \"$dir\\subdir\\subdummydir\" -itemtype directory | out-null }",
        "if (!(test-path \"$dir\\subdir\\subdummy.txt\")) { new-item -force \"$dir\\subdir\\subdummy.txt\" -itemtype file | out-null }",
    ],
    "persist": [
        "dummy.txt",
        "dummydir",
        "subdir\\subdummydir",
        "subdir\\subdummy.txt"
    ]
}
```
So no need to strip directories of source for target anymore.

To participate in the code review and tests, go visit https://github.com/h404bi/scoop-persist-test for test cases.