terminal: remove deprecated activateTerminal method

[vince-fugnitto]

Feature Description:

The activateTerminal method has been deprecated (~3 years) and should be removed from the codebase.
References to activateTerminal should be updated to instead use open.

theia/packages/terminal/src/browser/base/terminal-service.ts

Lines 32 to 37 in 7f954ac

	/**
	* Display new terminal widget.
	* @param terminal - widget to attach.
	* @deprecated use #open
	*/
	activateTerminal(terminal: TerminalWidget): void;

Fixes:

theia/packages/task/src/browser/task-service.ts

Line 1059 in 7f954ac

this.terminalService.activateTerminal(terminal);

- this.terminalService.activateTerminal(terminal); 
+ this.terminalService.open(terminal); 

theia/packages/terminal/src/browser/terminal-frontend-contribution.ts

Line 402 in 7f954ac

this.activateTerminal(termWidget);

- this.activateTerminal(termWidget); 
+ this.open(termWidget); 

theia/packages/terminal/src/browser/terminal-frontend-contribution.ts

Lines 577 to 579 in 7f954ac

	activateTerminal(widget: TerminalWidget, widgetOptions?: ApplicationShell.WidgetOptions): void {
	this.open(widget, { widgetOptions });
	}

- activateTerminal(widget: TerminalWidget, widgetOptions?: ApplicationShell.WidgetOptions): void { 
-     this.open(widget, { widgetOptions }); 
- }