go.*,text,widget{,/material}: enable configurable line wrapping within words

This commit enables consumers of the text shaper to select a policy for how
line breaking candidates will be chosen. The new default policy can break lines
within "words" (UAX#14 segments) when words do not fit by themselves on a line.
This ensures that text does not horizontally overflow its bounding box unless
the available width is insufficient to display a single UAX#29 grapheme cluster.

Fixes: https://todo.sr.ht/~eliasnaur/gio/467
Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>

text/shaper.go

@@ -16,6 +16,27 @@ import (
 	"golang.org/x/image/math/fixed"
 )
 
+// WrapPolicy configures strategies for choosing where to break lines of text for line
+// wrapping.
+type WrapPolicy uint8
+
+const (
+	// WrapHeuristically tries to minimize breaking within words (UAX#14 text segments)
+	// while also ensuring that text fits within the given MaxWidth. It will only break
+	// a line within a word (on a UAX#29 grapheme cluster boundary) when that word cannot
+	// fit on a line by itself. Additionally, when the final word of a line is being
+	// truncated, this policy will preserve as many symbols of that word as
+	// possible before the truncator.
+	WrapHeuristically WrapPolicy = iota
+	// WrapWords does not permit words (UAX#14 text segments) to be broken across lines.
+	// This means that sometimes long words will exceed the MaxWidth they are wrapped with.
+	WrapWords
+	// WrapGraphemes will maximize the amount of text on each line at the expense of readability,
+	// breaking any word across lines on UAX#29 grapheme cluster boundaries to maximize the number of
+	// grapheme clusters on each line.
+	WrapGraphemes
+)
+
 // Parameters are static text shaping attributes applied to the entire shaped text.
 type Parameters struct {
 	// Font describes the preferred typeface.
@@ -32,6 +53,9 @@ type Parameters struct {
 	// truncated.
 	Truncator string
 
+	// WrapPolicy configures how line breaks will be chosen when wrapping text across lines.
+	WrapPolicy WrapPolicy
+
 	// MinWidth and MaxWidth provide the minimum and maximum horizontal space constraints
 	// for the shaped text.
 	MinWidth, MaxWidth int
@@ -318,6 +342,7 @@ func (l *Shaper) layoutParagraph(params Parameters, asStr string, asBytes []byte
 		locale:        params.Locale,
 		font:          params.Font,
 		forceTruncate: params.forceTruncate,
+		wrapPolicy:    params.WrapPolicy,
 		str:           asStr,
 	}
 	if l, ok := l.layoutCache.Get(lk); ok {