Fix TextEdit clips children and focus style.

[WhalesState]

This PR refactors TextEdit to stop clipping its children and now uses its own CanvasItem logic for drawing text.

Changes:

• TextEdit no longer clips child nodes.
• Custom CI-based drawing is used for rendering text in TextEdit.
• Custom CI-based drawing is used for rendering code completion in CodeEdit.

Note: This PR is not intended to change any existing behavior due to the complexity of the TextEdit class. The only goal is to resolve the mentioned issues and improve internal drawing consistency.

• Fixes: TextEdit text is not clipped into content margin. #42342
• Fixes: TextEdit always clips content (including the focus outline, causing it to be not fully visible) #32996
• Fixes: Expand Margin is not working in Styles for TextEdit #74445

[kitbdev]

I don't know much about the rendering server methods to add canvas items, but it seems to work fine.

Some minor issues:

CodeEdit::_draw_guidelines still uses theme_cache.style_normal.

TextEdit::set_editable should call update_minimum_size().

[WhalesState]

This sounds kind of like #79735 but offset the other way.

The half line spacing we add to offset the text should be removed or double checked if it's taken into account in all other calculations like _get_visible_lines_offset and get_visible_line_count.

[WhalesState]

Moved the styles fix to another PR #110527, will keep this PR fixing only the clipping issues.

[kitbdev]

The half line spacing we add to offset the text should be removed or double checked if it's taken into account in all other calculations like _get_visible_lines_offset and get_visible_line_count.

I think it will have to be considered there. I've been looking for some inconsistency with related calculations, so thanks for pointing that out. This can be done later though, the behavior in #110527 get_line_column_at_pos is good for now. It can be more easily seen with the cross cursor.

[kitbdev]

Looks good.

• This also fixes #74445 since the expand margins now work by default .
• I don't think this fixes #42342 I think it is talking about how the text doesn't get clipped accurately when there is a content margin on a per pixel bases, though it is hard to tell.

Note that TextEdit's clip_contents default value changed, but this is needed to fix the issues.

[Repiteo]

Thanks!