TextSplitter: don't mutate 'words'

I was puzzled by why the dictionary words were sorted by length.
It was because TextSplitter sorted its parameter, instead of a copy.

This doesn't affect encoding size, but does affect the encoding NUMBER
of the found words.  We'll deliberately restore sorting by length next,
for other reasons, but not by spooky action.

py/makeqstrdata.py

@@ -280,7 +280,7 @@ def translate(translation_file, i18ns):
 
 class TextSplitter:
     def __init__(self, words):
-        words.sort(key=lambda x: len(x), reverse=True)
+        words = sorted(words, key=lambda x: len(x), reverse=True)
         self.words = set(words)
         if words:
             pat = "|".join(re.escape(w) for w in words) + "|."