selection style issue in "RTL" direction

[hamedmoradidev]

I’m having an issue with react-spreadsheet in an RTL project.
When the user selects cells, the --selected class causes an overflow problem:

1. The blue highlight (that indicates the selected cells) is not aligned properly.

‌2. Around 80% of the blue area is pushed out of view to the right and requires scrolling to see it.

You can reproduce the problem by setting the table’s direction to "rtl" and then trying to select or copy all (or part of) the data.

[iddan]

I'd be happy to merge a PR