Fixes #4150 - Finish implementing Line View (#4260)

* Initial plan

* Add comprehensive analysis of Line implementation status

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Complete Line implementation with documentation, example, and tests

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Add PR summary documenting Line implementation completion

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Add comprehensive completion report for Issue 4150

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Fix Line rendering: use SuperView's LineCanvas instead of own

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Redesign Line to use Border instead of manual LineCanvas

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Add Line.Style property to avoid BorderStyle conflict

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Add SetWidth/SetHeight methods to preserve dimensions on Orientation change

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Implement CWP events for Width/Height properties; update Line to use events

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* WIP: Updating Line.
Cleaned up Layout tests.

* Made Height/Width non-nullable

* Add doWork stage to CWPPropertyHelper to execute between Changing and Changed events

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Move ViewLayoutEventTests to parallelizable tests without AutoInitShutdown

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Replace tracking fields with Length property for thread-safe Line implementation

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Fix orientation handling to preserve user-set dimensions in object initializers

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Simplify orientation handling with dimension swapping - all tests passing

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Add Length backing field and fix object initializer dimension handling

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Use CWP OnChanging events to manage dimensions instead of OnChanged

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Move LineTests to parallelizable; simplify tests with GetAnchor; fix Length property

Co-authored-by: tig <585482+tig@users.noreply.github.com>

* Code cleanup.

* Code cleanup.

* Update Terminal.Gui/ViewBase/View.Layout.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update Terminal.Gui/ViewBase/View.Layout.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update Terminal.Gui/ViewBase/View.Layout.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update Terminal.Gui/ViewBase/View.Layout.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Fixed nullable warning in test

* Removed PR files and updated copilot guidance

* Reverted .gitignore change

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Tig <tig@users.noreply.github.com>
Co-authored-by: tig <585482+tig@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Terminal.sln

@@ -1,7 +1,7 @@
 
 Microsoft Visual Studio Solution File, Format Version 12.00
-# Visual Studio Version 17
-VisualStudioVersion = 17.2.32427.441
+# Visual Studio Version 18
+VisualStudioVersion = 18.0.11018.127 d18.0
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Terminal.Gui", "Terminal.Gui\Terminal.Gui.csproj", "{00F366F8-DEE4-482C-B9FD-6DB0200B79E5}"
 EndProject
@@ -34,6 +34,7 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "GitHub", "GitHub", "{13BB2C
 		.github\workflows\api-docs.yml = .github\workflows\api-docs.yml
 		.github\workflows\build-release.yml = .github\workflows\build-release.yml
 		.github\workflows\check-duplicates.yml = .github\workflows\check-duplicates.yml
+		copilot-instructions.md = copilot-instructions.md
 		GitVersion.yml = GitVersion.yml
 		.github\workflows\integration-tests.yml = .github\workflows\integration-tests.yml
 		.github\workflows\publish.yml = .github\workflows\publish.yml