Add a test for letter spacing.

This test is approximate because the 0.5px test is off by 1px in terms of height.

core/tests/regression_tests.rs

@@ -211,6 +211,7 @@ swf_tests_approx! {
     (stage_object_properties, "avm1/stage_object_properties", 4, 0.051),
     (stage_object_properties_swf6, "avm1/stage_object_properties_swf6", 4, 0.051),
     (movieclip_getbounds, "avm1/movieclip_getbounds", 1, 0.051),
+    (edittext_letter_spacing, "avm1/edittext_letter_spacing", 1, 1.0),
 }
 
 /// Wrapper around string slice that makes debug output `{:?}` to print string same way as `{}`.

core/tests/swfs/avm1/edittext_letter_spacing/output.txt

@@ -0,0 +1,15 @@
+//Creating left aligned text w/ wordwrap, multiline & long text
+//field.textWidth
+388
+//field.textHeight
+60
+//Creating left aligned text w/ wordwrap, multiline, 0.1px letter spacing & long text
+//field.textWidth
+397
+//field.textHeight
+60
+//Creating left aligned text w/ wordwrap, multiline, 0.5px letter spacing & long text
+//field.textWidth
+398
+//field.textHeight
+75