Problem:
The CST printer emits trailing whitespace after multiline text nodes.
With 1704c60 and `:cst` corpus tests
this causes trailing spaces to appear on `test --update`.
These spaces cannot be removed afterward, as the test runner
expects an exact character-for-character match for CST tests.

Solution:
Print whitespace only if node is not multiline.

(cherry picked from commit 4ac2d5d)