Allow closing notifications with middle mouse button

[martijnrondeel]

Using the middle mouse button click on a notification to close it makes the process a bit quicker instead of searching for the small x button.

[vscodebot]

(Experimental duplicate detection)
Thanks for submitting this issue. Please also check if it is already covered by an existing one, like:

• Middle mouse button doesn't scroll editor window (#40985)
• Allow middle mouse button to be bound in keyboard shortcuts (#43794)
• Middle mouse button invokes column selection and selection paste on Linux at the same time (#49693)

[martijnrondeel]

Thank you @bpasero for implementing this 👍