Fix TextEdit::get_line_count() when lines are wrapped

[kopcion]

After this PR TextEdit::get_line_count() will return the number of entries in text vector, as well as a number of times those lines wrap around so that the result is the same as what users can see on screen, as opposed to a number of '\n' characters.

Bugsquad edit: Fixes #38180.

[YeldhamDev]

Please use a more descriptive commit message.

[kopcion]

I hope this commit message is more descriptive :)

[akien-mga]

To clarify about the commit message, we usually favor having a commit title that accurately describe what the fixed bug is, instead of only pointing to a GitHub issue number (which can't be read through git log). See https://github.com/godotengine/godot/blob/master/CONTRIBUTING.md#format-your-commit-messages-with-readability-in-mind

So here something like this would be great:

Fix TextEdit::get_line_count() when lines are wrapped

TextEdit::get_line_count() now considers visible lines instead of lines in source
text before wrapping by adding for each line TextEdit::times_line_wraps(int).

Fixes #38180.

Using "Fixes #issue" in the commit description / PR description also means that GitHub will automatically close the issue when the PR is merged: https://help.github.com/en/github/managing-your-work-on-github/closing-issues-using-keywords

[Paulb23]

This is more of a enhancement then bug, get_line_count is used for looping over the "raw" lines outside of TextEdit and a couple places internally. Got some notes down for #31739, where instead we create new method called get_visual_line_count that handles not only wrapping but hidden lines as well.

[Paulb23]

Closing as superseded by #50371 which exposed get_total_visible_line_count to do this.