Change Font::offsetForPositionForComplexText to use CachingWordShapeIterator

LayoutTests/editing/selection/offset-from-point-expected.txt

Index: LayoutTests/editing/selection/offset-from-point-expected.txt
diff --git a/LayoutTests/editing/selection/offset-from-point-expected.txt b/LayoutTests/editing/selection/offset-from-point-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..29b8903086bbd6e5b0df5170cb224ad256f85527
--- /dev/null
+++ b/LayoutTests/editing/selection/offset-from-point-expected.txt
@@ -0,0 +1,108 @@
+12 345 6789
+12 345 6789
+12 345 6789
+12 345 6789
+LTR
+0=-1 (-1)
+1=11 (12)
+2=31 (20)
+3=51 (20)
+4=71 (20)
+5=91 (20)
+6=111 (20)
+7=131 (20)
+8=151 (20)
+9=171 (20)
+10=191 (20)
+11=211 (20)
+LTR (Complex Path)
+0=-1 (-1)
+1=11 (12)
+2=31 (20)
+3=51 (20)
+4=71 (20)
+5=91 (20)
+6=111 (20)
+7=131 (20)
+8=151 (20)
+9=171 (20)
+10=191 (20)
+11=211 (20)
+RTL
+11=-1 (-1)
+8=11 (12)
+9=31 (20)
+10=51 (20)
+7=71 (20)
+6=90 (19)
+4=111 (21)
+5=131 (20)
+3=151 (20)
+2=170 (19)
+1=191 (21)
+0=211 (20)
+RTL (Complex Path)
+11=-1 (-1)
+8=11 (12)
+9=31 (20)
+10=51 (20)
+7=71 (20)
+6=91 (20)
+4=111 (20)
+5=131 (20)
+3=151 (20)
+2=171 (20)
+1=191 (20)
+0=211 (20)
+VERTICAL-LR
+0=-1 (-1)
+1=11 (12)
+2=31 (20)
+3=51 (20)
+4=71 (20)
+5=91 (20)
+6=111 (20)
+7=131 (20)
+8=151 (20)
+9=171 (20)
+10=191 (20)
+11=211 (20)
+VERTICAL-LR (Complex Path)
+0=-1 (-1)
+1=11 (12)
+2=31 (20)
+3=51 (20)
+4=71 (20)
+5=91 (20)
+6=111 (20)
+7=131 (20)
+8=151 (20)
+9=171 (20)
+10=191 (20)
+11=211 (20)
+VERTICAL-RL
+0=-1 (-1)
+1=11 (12)
+2=31 (20)
+3=51 (20)
+4=71 (20)
+5=91 (20)
+6=111 (20)
+7=131 (20)
+8=151 (20)
+9=171 (20)
+10=191 (20)
+11=211 (20)
+VERTICAL-RL (Complex Path)
+0=-1 (-1)
+1=11 (12)
+2=31 (20)
+3=51 (20)
+4=71 (20)
+5=91 (20)
+6=111 (20)
+7=131 (20)
+8=151 (20)
+9=171 (20)
+10=191 (20)
+11=211 (20)