pixel perfect layout

Today, all plugins are constrained to a grid. It would be good to have a pixel perfect mode that could enable folks to absolutely position plugins. If this is a mode that can be toggled on for individual plugins (which would probably be ideal) then we could give it a hotkey so that when holding the key and moving a plugin you simply get a pixel grid instead of the default grid.

No files, tests, or entry points are named. Start by locating the plugin layout and grid-positioning code, then determine how individual plugin modes and the proposed hotkey should interact. Done means plugins can be positioned at pixel-level precision without breaking the existing grid behavior.

Written by the indexing model from the issue text.