fix: Remove assert_eq! from BiDi ShapeLine for avoid crash

[NSTikhomirov]

Cosmic-text can crash when certain characters show up in the editor view.

Error message:

thread 'main' panicked at /home/user/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/cosmic-text-0.19.0/src/shape.rs:1359:13:
assertion `left == right` failed
  left: false
 right: true

Reproduce steps (commit c24886c2471e5606587c46090cd25dbbf209186b):

printf 'A\034\327\220\n' > /tmp/bidi.txt
./editor-test.sh /tmp/bidi.txt

As I understand it, the assert expects all paragraphs in a line to have the same direction.
But for arbitrary text that's not always true, a line can split into paragraphs with different directions, and then it crashes on normal input.

And it seems this direction isn't really needed for correctness: the character order comes from the BiDi levels themselves, while the line direction is more for alignment and the ellipsis.
So I just removed the assert and shape the line by its base direction. No more panic, and normal lines look the same as before.

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