tests/cpydiff: Add case for str.ljust/rjust.

tests/cpydiff/types_str_ljust_rjust.py

@@ -0,0 +1,7 @@
+"""
+categories: Types,str
+description: str.ljust() and str.rjust() not implemented
+cause: MicroPython is highly optimized for memory usage. Easy workarounds available.
+workaround: Instead of `s.ljust(10)` use `"%-10s" % s`, instead of `s.rjust(10)` use `"% 10s" % s`. Alternatively, `"{:<10}".format(s)` or `"{:>10}".format(s)`.
+"""
+print('abc'.ljust(10))