Prefer resolving to PATHEXT extensions on Windows

[dsherret]

The command in the config here (#23 (comment)):

"exec": {
    "associations": [
      "**/*.{sh,bash}",
      "**/package.json"
    ],
    "prettier-package-json.associations": "**/package.json",
    "prettier-package-json": "node_modules/.bin/prettier-package-json"
  },

...has files prettier-package-json, prettier-package-json.cmd and prettier-package-json.ps1, but doesn't work on Windows:

Error formatting V:\scratch-npm\package.json. Message: Cannot start formatter process: %1 is not a valid Win32 application. (os error 193)

...unless the .cmd extension is provided. It should work cross platform and not require this extension.

[mahtaran]

Ran into this issue while trying to integrate the Dart formatter (the Dart CLI is provided by a dart.bat file). This does seem to be the intended behaviour of Rust's std::process::Command though, due to the associated security concerns (source):

The search path to be used may be controlled by setting the PATH environment variable on the Command, but this has some implementation limitations on Windows (see issue rust-lang/rust#37519).

Platform-specific behavior

Note on Windows: For executable files with the .exe extension, it can be omitted when specifying the program for this Command. However, if the file has a different extension, a filename including the extension needs to be provided, otherwise the file won’t be found.

See also: rust-lang/rust#123728 and rust-lang/rust#94743

One way around this would be to use the which crate, which returns the absolute path to an executable while respecting Windows's PATHEXT environment variable.