Improve modal behavior

[FrederikBolding]

This PR does two things to improve the modal behavior:

• Firstly it enables preserveScrollBarGap, this is supposed to be enabled by default in Chakra according to the documentation, but isn't. This prevents the page jumping around when modals are opened.
• Secondly it patches @chakra-ui/focus-lock to prevent scrolling when returning focus (e.g. when closing a modal). Chakra uses react-focus-lock under the hood which supports not scrolling, but this functionality is not currently supported in Chakra.

[github-actions[bot]]

Commit 094934fda0089ef50871f082d3e0941bf8baec51 successfully pushed to staging website:

https://metamask.github.io/snaps-directory-staging/pr/363/