Update mysterium.json to add ISO compatibility, fix incorrectly sized keys and f row spacing

[coseyfannitutti]

Description

Adds ISO compatibility to the layouts on VIA for rev1.1 PCB and fixes some incorrectly sized keys and corrects f-row spacing to look more like the physical layout.

Pinout has not changed and will work with both the rev1 PCB and firmware as well.

QMK Pull Request

qmk/qmk_firmware#10348 (merged)

Checklist

• The QMK source code follows the guide here: https://caniusevia.com/docs/configuring_qmk
• The VIA definition follows the guide here: https://caniusevia.com/docs/layouts
• I have tested this keyboard definition using VIA's "Design" tab.
• I have tested this keyboard definition with firmware on a device.
• I have assigned alpha keys and modifier keys with the correct colors.
• The Vendor ID is not 0xFEED