Add ytickangle and ztickangle functions (bug #59067) * scripts/plot/appearance/ytickangle.m: New function. * scripts/plot/appearance/ztickangle.m: New function. * scripts/plot/appearance/module.mk: Add ytickangle.m, ztickangle.m to build system. * NEWS: Announce addition of xtickangle, ytickangle, ztickangle functions. * doc/interpreter/plot.txi: Add xtickangle to manual and XREF anchors for ytickangle and ztickangle. * __unimplemented__.m: Remove xtickangle, ytickangle, ztickangle from unimplemented list. * __tickangle__.m: Fix empty figure popping up during BIST tests.

--- a/NEWS	Wed Nov 04 19:55:43 2020 -0800
+++ b/NEWS	Wed Nov 04 20:18:11 2020 -0800
@@ -169,6 +169,9 @@
 * `rng`
 * `startsWith`
 * `streamribbon`
+* `xtickangle`
+* `ytickangle`
+* `ztickangle`
 
 ### Deprecated functions and properties