DevTools: Make the selected commit label editable

[zhusiyi111]

Make the selected commit label to be editable, so that developers can switch the commit index conveniently.

Here is the effect:

[sizebot]

Comparing: 1a106bd...020a6f9

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.min.js	=	126.89 kB	126.89 kB	=	40.69 kB	40.69 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	129.70 kB	129.70 kB	=	41.61 kB	41.61 kB
facebook-www/ReactDOM-prod.classic.js	=	406.00 kB	406.00 kB	=	75.07 kB	75.07 kB
facebook-www/ReactDOM-prod.modern.js	=	394.35 kB	394.35 kB	=	73.25 kB	73.25 kB
facebook-www/ReactDOMForked-prod.classic.js	=	406.00 kB	406.00 kB	=	75.07 kB	75.07 kB

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

Generated by 🚫 dangerJS against 020a6f9

[zhusiyi111]

@bvaughn Hi, what's your opinion about this PR？

[bvaughn]

I think if we move forward with a feature like this, I'll go with #19957 since it was opened first. Thanks for understanding!