Fix readFile bindings

[tjdett]

Neither FileHandle.readFile or FileHandle.readFileWith worked, as their definitions were incorrect.

Tests have been added to verify expected behaviour.

[TheSpyder]

Note that FileHandle.read won't work either, it takes an options object not a series of parameters: https://nodejs.org/api/fs.html#fs_filehandle_read_options

However we only needed to fix readFile for our use case and we might end up down a rabbit hole trying to fix more than we need.

[sikanhe]

Doesn't readFile take an optional object? https://nodejs.org/api/fs.html#fs_filehandle_readfile_options

[sikanhe]

@TheSpyder We will fix those asap

[TheSpyder]

Doesn't readFile take an optional object? https://nodejs.org/api/fs.html#fs_filehandle_readfile_options

Yes, but it doesn't need to. It's <Object> | <string>, and later the docs say

If options is a string, then it specifies the encoding.

[sikanhe]

The whole nodejs api design is just nuts 😅