Fix horizontal_wrapping row height after using text_edit_multiline (#8000)

* [x] I have followed the instructions in the PR template

This PR have two commits:
* **First commit** - introduction of tests and their canonization image.
Expected behaviour is that `horizontal_wrapped_multiline_row_height`
would match `horizontal_wrapped_multiline_row_height_reference`, but it
doesn't. There is a bug in `horizontal_wrapped` that breaks line height
after using `text_edit_multiline`.
* **Second commit** - fix. You can see that
`horizontal_wrapped_multiline_row_height` now looks like
`horizontal_wrapped_multiline_row_height_reference` (although it's not a
perfect match, upd: found, this is because of this issue:
https://github.com/emilk/egui/issues/4921).

I have used LLM to help me with this PR (codex + claude code).

BTW, I'm using horizontal_wrapped with end_row instead of vertical +
horizontal alternation, because I automatically generate my UI through
some complex interactions between elements in my code, and it's can be
that my `horizontal` starts in one function, and ends in another.
Something like `begin_horizontal`/`end_horizontal`/`get_current_layout`
would be very handy, related to
https://github.com/emilk/egui/issues/1004.

Also, I would like indent to be supported in `horizontal_wrapped`, or
also, to have `indent_start`/`indent_end`. This is why I used
`monospace("| ")` in my example, it simulates my use-case.

tests/egui_tests/tests/snapshots/horizontal_wrapped_multiline_row_height.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:ef21b42f90401f6b85685e1cc37d07970b38d2b40394f53bbde5bd4f0d54fb95
+size 5340

tests/egui_tests/tests/snapshots/horizontal_wrapped_multiline_row_height_reference.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:5025f4cb528ae5edc387149f1d14523ab4b93058f0862e775a1c2276a3e77af6
+size 5377