Do not do type assertion in widgets/text_tools.go

[redstarcoder]

Currently fillStringAtWidget, fillStringAtWidthCursor, and cursor.MoveToX do a type assertion on gc to make it into *draw2dgl.GraphicContext. This is because they rely on gc.Current.Scale and loadCurrentFont which relys on gc.LoadFont (Neither of which can be accessed from a draw2d.GraphicContext interface as of this writing). We need a substitute or a change in the draw2d API to fix this.

[redstarcoder]

The outcome of llgcode/draw2d#116 could influence this issue.