Avoid cloning Rows during Galley::concat

[afishhh]

Moves ends_with_newline into PlacedRow to avoid clones during layout.
I don't think there was a rationale stronger than "don't change too much" for not doing this in #5411, so I should've just done this from the start.
This was a significant part of the profile for text layout (as it cloned almost every Row, even though it only needed to change a single boolean).

Before:

After:

(note that these profiles focus solely on the top-level Galley::layout_inline subtree, also don't compare sample count as the duration of these tests was completely arbitrary)

egui_demo_lib *text_layout* benches:

• I have followed the instructions in the PR template

(As usual, the tests fail for me even on master but the failures on master and with these changes seem the same :))

[github-actions]

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