Fixes #4312. Write ViewArrangement tests (#4313)

* Initial plan

* Add comprehensive ViewArrangement unit tests

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

* Add more comprehensive ViewArrangement tests

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

* Add view-specific arrangement tests and documentation

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

* Add MouseGrabHandler tests proving concurrent testing works

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

* Add proposal for Application.RaiseMouseEvent refactoring

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

* Add interface design discussion to proposal

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

* Update proposal with final interface naming: IMouseGrab and IMouse

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

* Remove refactoring proposal - will be done in separate PR

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

* Fix build after v2_develop merge - replace Application.MouseGrabHandler with Application.Mouse

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

* Add 14 more ViewArrangement tests covering flag combinations and edge cases

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

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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>

Author: Copilot