RenderBox performs some trimming inside of constrainBlockMarginInAvailableSpaceOrTrim and computeOrTrimInlineMargin as the renderer goes through layout. This has some unfortunate side effects, such as requiring us to set the rare data bits to indicate the margin has been trimmed at the same location. This action requires a const_cast that could be avoided since trimming should not occur at the RenderBox level and should be occurring completely in the layout system it is in (flex, grid, or block). We should make sure that the trimming logic is contained wholly within each layout system and should remove this logic from RenderBox once it is