Fix text editing capabilities

[kunitoki]

This pull request significantly improves the handling of empty paragraphs and caret/selection logic in the StyledText class, especially around consecutive newlines and edge cases involving line navigation and caret positioning. It also introduces new APIs for line navigation and value retrieval in result types.

Major improvements include:

StyledText caret and selection improvements

• Improved caret placement and selection logic for empty paragraphs (consecutive newlines), ensuring correct caret rendering and navigation in these cases, and fixing several bugs related to caret position at the end of text or on empty lines. [1] [2] [3] [4]
• Refactored getGlyphIndexAtPosition to better handle clicks on empty lines and paragraphs, and to use a more robust line selection algorithm. [1] [2] [3]
• Added two helper methods, findParagraphNewlinePosition and findParagraphNewlinePositionByIndex, to reliably map between visual lines/paragraphs and character indices for newlines. [1] [2]

New API and navigation features

• Introduced getGlyphIndexOnAdjacentLine for moving the caret vertically between visual lines, treating soft-wrapped and explicit lines equivalently. [1] [2]
• Improved initialization and tracking of line heights and paragraph offsets to ensure consistent layout and navigation, especially for empty paragraphs. [1] [2] [3] [4] [5] [6]

ResultValue utility

• Added valueOr overloads to ResultValue, supporting both copy and move semantics for retrieving the stored value or a default, improving ergonomics when working with result types.

[codecov]

Codecov Report

❌ Patch coverage is 54.59459% with 168 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.49%. Comparing base (901f930) to head (17417f0).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
modules/yup_gui/widgets/yup_TextEditor.cpp	51.12%	65 Missing ⚠️
modules/yup_graphics/fonts/yup_StyledText.cpp	69.54%	53 Missing ⚠️
modules/yup_gui/native/yup_Windowing_sdl2.cpp	0.00%	41 Missing ⚠️
modules/yup_gui/keyboard/yup_TextInputTarget.cpp	0.00%	6 Missing ⚠️
modules/yup_gui/component/yup_Component.cpp	40.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #96      +/-   ##
==========================================
+ Coverage   73.17%   73.49%   +0.32%     
==========================================
  Files         573      573              
  Lines       56342    56596     +254     
==========================================
+ Hits        41229    41598     +369     
+ Misses      15113    14998     -115     

Files with missing lines	Coverage Δ
modules/yup_core/misc/yup_ResultValue.h	100.00% <100.00%> (ø)
modules/yup_graphics/fonts/yup_StyledText.h	100.00% <ø> (ø)
modules/yup_gui/component/yup_ComponentNative.h	0.00% <ø> (ø)
modules/yup_gui/keyboard/yup_TextInputTarget.h	100.00% <ø> (ø)
...ules/yup_gui/themes/theme_v1/yup_ThemeVersion1.cpp	38.38% <100.00%> (ø)
modules/yup_gui/widgets/yup_TextEditor.h	71.42% <ø> (ø)
modules/yup_gui/component/yup_Component.cpp	58.33% <40.00%> (ø)
modules/yup_gui/keyboard/yup_TextInputTarget.cpp	22.72% <0.00%> (+22.72%)	⬆️
modules/yup_gui/native/yup_Windowing_sdl2.cpp	8.50% <0.00%> (-0.29%)	⬇️
modules/yup_graphics/fonts/yup_StyledText.cpp	77.75% <69.54%> (+10.32%)	⬆️
... and 1 more

... and 4 files with indirect coverage changes

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