filesystem(perf): allow deleting entire filesystem in one non-recursive operation

## Feature Request

### Plugin

Filesystem

### Description

Currently, at least on the Web implementation of the FIlesystem plugin, it appears that the only way to delete the contents of a filesystem path is to delete the entire IndexedDB manually. Unless I am missing something.

There is of course the `rmdir('/', { recursive: true })` operation, but this appears to iterate through every entry very very very slowly. If there are a significant number of entries, this operation can take minutes to finish.

It would be nice if there were a `clear()` operation, or if the existin `delete` allowed a more efficient operation.

### Platform(s)

Web (Ios/Android optional as those seem much faster, but for parity I would assume you'd want it on all platforms.)

### Preferred Solution

Either make `rmdir` more efficient on Web, or provide a `clear()` operation that deletes the database entirely on Web, and on other platforms it would clear the specified `FilesystemDirectory`.

### Alternatives

Not sure, open to suggestions.

I suppose you could use open an IndexedDB handle on web, then issue a delete operation using the key value, instead of using recursion:
https://github.com/ionic-team/capacitor-plugins/blob/main/filesystem/src/web.ts#L357

### Additional Context