Tooltip spec changes

[SamBent]

• .NET Core Version: (e.g. 3.0 Preview1, or daily build number, use dotnet --info) 6.0
• Windows version: (winver) all
• Does the bug reproduce also in WPF for .NET Framework 4.8?: No
• Is this bug related specifically to tooling in Visual Studio (e.g. XAML Designer, Code editing, etc...)? no
• Security issues and bugs should be reported privately, learn more via our responsible disclosure guidelines.

Problem description:
The accessibility working group has asked for changes in the tooltip behavior:

• Typing Ctrl should dismiss any open tooltip. (Was: Ctrl dismisses the tooltip owned by the control with focus.)
• Typing ESC should dismiss any open tooltip. (Was: ESC does not affect tooltips.)

This means amending the spec, then implementing the changes.

Notes:
The working group says "Esc may have consequences beyond the tooltip, and the user would be taking that responsibility on if they do not choose to use Ctrl."

It is currently not possible to honor these requirements when the tooltip comes from an inactive (background) window, which doesn't receive keyboard input. Extending the behavior to this case requires help from the OS.