Path: Should `normalize()` remove trailing slashes?

**Is your feature request related to a problem? Please describe.**

I'm trying to find out if a file is inside a specific directory. My plan was to do it like this:

```js
import { common } from "https://deno.land/std@0.148.0/path/mod.ts";
function insideDir(file, dir) {
const result = common([file, dir]);
return result == dir;
}
```

However, this doesn't work if the `dir` argument doesn't contain a trailing slash. For example:
```js
common(["/path/to/dir", "/path/to/dir/file.txt"]);
```
returns `"/path/to/dir/"`, and `"/path/to/dir/" != "/path/to/dir"`

**Describe the solution you'd like**

If I'm not mistaken, `/path/to/dir` and `/path/to/dir/` both point to the same thing. If so, then wouldn't it make sense to have a function that removes trailing slashes from paths? Maybe `normalize()` would be a good fit for this.

**Describe alternatives you've considered**

- Add a function to std that performs this exact algorithm
- Make `common()` remove the trailing slash
- It seems `resolve()` also removes trailing slashes, though passing just a single command isn't really documented anywhere (and neither does it contain tests for this case)