Prep for Release v1.9.0

[tig]

This PR is in prep for Release v1.9.0.

We're moving to 1.9 because

Given a version number MAJOR.MINOR.PATCH, increment the:

MAJOR version when you make incompatible API changes
MINOR version when you add functionality in a backwards compatible manner
PATCH version when you make backwards compatible bug fixes
Additional labels for pre-release and build metadata are available as extensions to the MAJOR.MINOR.PATCH format.

Current list of PRs included since v1.8.2:

• Added a mainloop unit test with a task. #2168
• Fixes #2163 and #2140 - ListView: OnSelectedChanged is called when it didn't actually change (again) #2164
• Revert "TreeView: Now highlights only model text" #2159
• Fixes #2156 - BREAKING CHANGE - Fixes IsOverridden and makes it internal #2158
• Fixes #1743 - CharMap renders painfully slow #2157
• TreeView: Now highlights only model text #2155
• Fixes #2140. OnSelectedChange is being called from OnEnter when the selection didn't actually change. #2152
• Bump coverlet.collector from 3.1.2 to 3.2.0 #2148
• Bump actions/setup-dotnet from 3.0.2 to 3.0.3 #2147
• Bump gittools/actions from 0.9.14 to 0.9.15 #2146
• Fixes 2142. Dim.Combine wasn't calculating well. #2145
• Some refactoring of the unit tests #2143
• Refactors UI Catalog to clean up old code and make more readable #2141
• Fixes #2137. Disabled menu item is selected on click. #2138
• Fixes #2135. Character Map scenario doesn't show the content view. #2136
• Fixes #2133. TreeView: desiredCursorVisibility field is set before the if condition check. #2134
• Adds CollectionNavigator to enable searching ListView/TreeView with keyboard #2132
• Fixes #2121. ContextMenu: When open, Shift-F10 should close menu. #2130
• Fixes #2122. Weird visual artifacts on clearing. #2124
• Fixes #2120. TreeView: Hide cursor in single select mode by default, add cursor toggle to TreeViewFileSystem Scenario #2123
• Fixes #2118. Enables HotColor for hotkeys on non-activated menus #2119
• Fixes #2109. MenuBar has extra space on left. Refactors MenuTests. Better Menu API docs. #2117
• Fixes tons of little View API doc typos  #2112
• Update 'Sample Usage' README.md section #2111
• Makes Notepad look better and fixes bugs #2107
• Improves the TabView minimum size and added more unit tests. #2105
• Fixes 2094. View does not clear it's background. #2104
• Simplify MakePrintable by using AND and avoiding converting to string #2101
• Fixes #2096. Makes RootMouseEvent cancellable #2100
• Added Rider/Resharper IDE settings (formatting, style) #2099
• Cleanups up and fixes docs in View class. #2098
• Added template docs to readme #2093
• Bump gittools/actions from 0.9.13 to 0.9.14 #2092
• Bump actions/setup-dotnet from 3.0.1 to 3.0.2 #2091
• Update readme #2087
• Fixes #433. Replaces demo.cs with standalone Example.cs #2084
• Fixes #2073. Fixes regression introduced in v1.8.2: Nesting MainLoop.Invoke deadlocks #2083
• Fixes #2081. Clipboard unit tests sometimes fail with WSL. #2082
• Bump actions/setup-dotnet from 2.1.1 to 3.0.1 #2080
• Fixes #2071. DrawContentComplete event is never called from the base if it's overridden. #2072
• Fixes #2069. Enable KeyDown and KeyUp events to be canceled (like KeyPress) #2070
• Bump ReactiveMarbles.ObservableEvents.SourceGenerator from 1.1.4 to 1.2.3 #2068
• Bump Microsoft.NET.Test.Sdk from 17.3.1 to 17.3.2 #2067
• Bump actions/setup-dotnet from 1 to 2.1.1 #2066
• Fixes #2064. Make Application.MouseGrabView public; allow views who use it some control #2065
• Fixes #2061. WindowsDriver - On 'MouseMoved', at least ReportMousePosition flag must be returned. #2063