fsPromises.cp(...) inconsistencies and bugs

The fsPromises.cp and fs.cp methods are inconsistent with the sync version because they do not correctly accept Buffer file paths. This also means it also improperly handles non-UTF8 encoded filenames. The sync variation supports Buffer. The method also does not appropriately validate inputs. Rather than throwing a proper Node.js type error when a Buffer is passed, it tries to use it and fails at another point deeper in the function. The impl of the async version of the method is also needlessly structured differently from the sync version leading to a fair amount of duplicated and inconsistent code, making it difficult to fix the inconsistencies. The sync version was updated recently to move significant pieces to C++ while the async versions were not similarly updated. Example: ```js fs.cpSync(Buffer.from('a'), Buffer.from('b')); // works! fs.cp(Buffer.from('a'), Buffer.from('b'), (err) => { /* ... */ }); // fails! ``` The error thrown is: ``` TypeError [ERR_INVALID_ARG_TYPE]: The "paths[0]" argument must be of type string. Received an instance of Buffer at resolve (node:path:1195:7) at normalizePathToArray (node:internal/fs/cp/cp:185:45) at isSrcSubdir (node:internal/fs/cp/cp:190:18) at checkPaths (node:internal/fs/cp/cp:110:32) at async cpFn (node:internal/fs/cp/cp:66:17) ``` `fs.cp(...)` is currently just a `callbackified(...)` version of `fsPromise.cp(...)`, so fixing one should fix the other: There are several fixes necessary: If `Buffer` is not going to be accepted, then the method should properly validate that the input `src` and `dest` are not Buffers and throw a proper `ERR_INVALID_ARG_TYPE` error. However, not accepting `Buffer` mean that the async versions of these will not properly handle non-UTF8 encoded file names. Ideally, the method would be updated to accept `Buffer` paths, but that means the `normalizePathToArray` method needs to be updated/refactored. Second, the differences that were introduced when the sync version was up…