`middle-click-popup`: variables in nested boolean previews hide the border of operators

[OneShot-Niko]

Description

This is often confusing whenever you forget about it due to the preview not displaying the starting (if the variable is at the start, otherwise, the ending border) border of the operator, which, unless you re-read your query again, can appear a bit confusing.

Steps to reproduce

1. enable middle-click-popup
2. make a variable
3. shift+click or CTRL+enter and then enter a string of nested booleans with the variable (e.g. "cos ((foo * 2) / 9))"
4. Notice that the variable is positioned in a way that hides the starting border of the operator that it's nested in.

Demonstration(s) and additional context

Seems to be caused by the fact that the variable is sized big enough that it is layered over the border of the operator.

Environment

Browser: LibreWolf 126.0.1-1 Scratch Addons version: 1.39.0-pre (6c89b40 - master) Operating system: win10 (32 bit) _{First encountered on Turbowarp Desktop 1.12.3 (addons version 40dafc4), made sure it still happens with ScratchAddons in Scratch's project editor.}