The rules for strings here are:
- 4 ASCII characters long
- Shorter ones are right-padded with spaces before use
- Trailing whitespace is always removed when serializing
We previously always padded them during parsing, which was incorrect.
This commit flips it around so we trim trailing whitespace when parsing.
We don't yet actually use this property's value for anything. Once we do
so, maybe we'll care more about them being stored as 4 characters
always, but for now this avoids us needing a special step during
computation.