This PR allows users to enable the tab bar in fullscreen mode.
A new setting; "showTabsFullscreen"; has been added which accepts a
boolean value. When `true`, then the tab bar will remain visible when
the terminal app is fullscreen. If the value is `false` (default), then
the tab bar is hidden in fullscreen.
When the tab bar is visible in fullscreen, the min/max/close controls
are hidden to maintain the expected behaviour of a fullscreen app.
## Validation Steps Performed
All unit tests are passing.
Manually verified that when the "launchMode" setting is "fullscreen" and
the "showTabsFullscreen" setting is `true`, the tab bar is visible on
launch.
Manually verified that changing the setting at runtime causes the tab
bar to be shown/hidden immediately (if the terminal is currently
fullscreen).
Manually verified that the new "showTabsFullscreen" setting is honoured
regardless of whether "showTabsInTitlebar" is set to `true` or `false`.
Closes#11130
27f775ee9e