PR: Add the Debug Cell icon to the debug toolbar

[stevetracvc]

Description of Changes

I added the "Debug Cell" icon to the toolbar.

• Wrote at least one-line docstrings (for any new functions)
• Added unit test(s) covering the changes (if testable)

• Included a screenshot or animation (if affecting the UI, see Licecap)

Before

After

I find it extremely annoying that all of the major Debug tools are in the toolbar except for the Debug Cell tool. And sometimes, when trying to click on it from the Debug menu, I accidentally hit the "Run File" toolbar icon instead. This PR adds the icon, keeping the same ordering that is used in the Debug menu.

Affirmation

By submitting this Pull Request or typing my (user)name below,
I affirm the Developer Certificate of Origin
with respect to all commits and content included in this PR,
and understand I am releasing the same under Spyder's MIT (Expat) license.

I certify the above statement is true and correct: stevetracvc

[impact27]

Looks good to me!

[dalthviz]

I guess this will need a rebase running something like #18691 (comment) but with master instead of 5.x right @impact27 ?

[stevetracvc]

I guess this will need a rebase running something like #18691 (comment) but with master instead of 5.x right @impact27 ?

Ok I was watching that other PR but wasn't 100% sure what I needed to do yet. I'll try that when I get home.

[stevetracvc]

I deleted and recreated this at #18877 since it was too big a hassle to figure out how to handle the CR issue for a one-line PR. 😄