debug: "Pause on breakpoint" is shown when pausing with "Pause (F6)"

[hyangah]

Originally reported in microsoft/vscode-go#3158.

When pausing the program with no breakpoints set with Pause F6, I see the UI say "paused on breakpoint" some of the times. I expect to see "paused on pause".
See the analysis @polinasok posted in the original report.

This is reproducible with Nightly & Insiders.

[gopherbot]

Change https://golang.org/cl/253578 mentions this issue: src/debugAdapter: send stopped events from continue on breakpoint only

[suzmue]

Fixed by cl/253578

[gopherbot]

Change https://golang.org/cl/262257 mentions this issue: src/debugAdapter: revert cl/253578