Fix: Prevent Middle Mouse Paste (#7035)

[Naresh-official]

Fixes #7035

Description

This PR fixes an issue where releasing the middle mouse button after panning on Linux causes an unintended paste action due to the system's primary clipboard behavior.

Changes Made

• Updated isMiddleButtonPressed function in blocksuite/affine/shared/src/utils/event.ts to properly detect middle-click for panning vs. pasting.
• Prevented pasting behavior if the middle mouse button was used for panning first.
• Added a check to differentiate between intentional pasting vs. panning release.
• Ensured compatibility across different platforms (Linux, Windows, macOS).

[CLAassistant]

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[graphite-app[bot]]

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[pengx17]

I think this PR can be safely closed and in favor of https://github.com/toeverything/AFFiNE/pull/11496? btw I searched for isMiddleButtonPressed and it seems it is not being used anywhere at all.