Improve communication of no debugger support when accessed via the activity bar

[per1234]

Is your feature request related to a problem? Please describe.

There is a very intriguing button in the place of honor in the Arduino IDE activity bar:

Unfortunately, many boards are not compatible with this feature, but this fact is not clear when accessing the debugger via the activity bar. When you try to use the debugger, there is no indication of why it's not working.

We saw that Pro IDE users were regularly running into this issue, for example:

• Alpha 0.0.5: Provide an example for configuring the debugger arduino-pro-ide#216 (comment)
• https://github.com/arduino/arduino-pro-ide/issues/219
• Does the arduino pro ide debugger supports arduino DUE? arduino-pro-ide#301
• macOS: debugger problem v0.1.1 arduino-pro-ide#328

An excellent improvement was made by disabling and adding a nice "Debugging is not supported by..." message when hovering over the debug button on the top bar (ATL-531), but I fear that users will bypass this by going straight for the activity bar.

Describe the solution you'd like

Any way to make it more clear that the debug feature is not available for the selected board when it is accessed via the activity bar button. For example:

• Disable the button.
• Show a "Debugging is not supported by..." message
• Require the user to enable debugging functionality via File > Preferences

Environment

OS: Windows 10
Version: 2.0.0-beta.2-snapshot.298cc11
Date: 2021-02-15T14:16:52.603Z
CLI Version: 0.16.0 alpha [c977a238]

[ubidefeo]

We should disable access to this sidebar when the selected board does not have debugging capabilities in the platform