Fix sorting of resources with numbers (numberish) titles

[turisap]

Hi,

I have encountered a possible bug. The bug is when we pass to <FullCalender /> react component (timeline view) resources
with titles as numbers or numberish strings like { title: 2 } or { title: '2' }.

Resolves #6427

My best guess is that in this case the last if statement in the flexibleCompare function gets executed. The problem is that String.localeCompare returns wrong values, f.e the following example returns 1

const a = '6'; 
const b = '12'; 
console.log(a.localeCompare(b));

but this return -1:

const a = '1'; 
const b = '12';  
console.log(a.localeCompare(b));

However, they should return the same value for sorting to work as expected.

You can find a runnable demo in this repo.

There is also a codesandbox with reduced example.

It looks like this:

It also can be solved by providing {numeric: true} as config param to localeCompare, but I am not sure which locale to pass in this case.