Overhaul node computeSize - use actual text width

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Node resize overhaul

• Precisely calculates node minimum size
• Prevents input & output overlap
• Prevents (normal*) widgets from rendering text over the edge of nodes
• Performance impact was sub-millisecond for normal usage in a 500-node graph

Minimum size for a few example node configurations

Widgets

• Converts hard-coded draw render values to class static properties
• Adds widget button draw function for left/right arrow widgets

* Exception: control_after_generate, as it is not a true input / widget. A check may be added later to handle this special case.

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Test failure is.. desirable! A group node that's now less insanely-huge; assuming due to widgets no longer stacking on outputs are now calculated.