config: show/hide close-tab button

[zummenix]

Config option to show/hide close-tab button in tabs.

I've moved the code responsible for creating X button in a separate function since it's already indented too far right, hope you don't mind.

Closes #3801

[pabohoney1]

I'm a new user to WezTerm and I'm hoping to fully switch to it soon. However this feature missing makes it a non-starter for me. Hopefully you can get some time to review this.

[sdemura]

I'd love to move to the 'fancy' tab bar, but without this 'fancy' is far uglier than the retro one...

[wez]

Thank you for this!
Rebased and pushed as a46bad1

For those making entitled remarks about not moving to wezterm because you find it ugly, please, by all means, use a different terminal emulator. You are not welcome here.

[pabohoney1]

Thank you for this! Rebased and pushed as a46bad1

For those making entitled remarks about not moving to wezterm because you find it ugly, please, by all means, use a different terminal emulator. You are not welcome here.

I don't find it ugly at all. I wanted the feature to prevent accidental closing of tabs, not to make it "prettier" =) Keep up the good work man, it is appreciated.