text,widget{,/material}: [API] move all shaping parameters into text.Parameters

This commit moves the min/max width of shaped text and the text's Locale into
text.Parameters. They were previously passed as separate function parameters to
the shaper, but this made little sense and added visual noise. This is a breaking
change, but only if you previously invoked the shaping API directly.

Callers of text.(*Shaper).LayoutString should change:

    shaper.LayoutString(params, minWidth, maxWidth, locale, "string")

to

    params.MinWidth=minWidth
    params.MaxWidth=maxWidth
    params.Locale=locale
    shaper.LayoutString(params, "string")

Callers of text.(*Shaper).Layout should do likewise.

Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>

widget/selectable_test.go

@@ -100,7 +100,7 @@ func TestSelectableConfigurations(t *testing.T) {
 					gtx.Constraints.Min = gtx.Constraints.Max
 				}
 				s := new(Selectable)
-				s.text.Alignment = alignment
+				s.Alignment = alignment
 				s.SetText(sentence)
 				interactiveDims := s.Layout(gtx, cache, font, fontSize, op.CallOp{}, op.CallOp{})
 				staticDims := Label{Alignment: alignment}.Layout(gtx, cache, font, fontSize, sentence, op.CallOp{})