Log points are special kinds of breakpoints that do not 'break' but instead log a message and then continue. This change implements basic log points that simply log the provided message, without any interpolation.
In order to resume execution after hitting a breakpoint, I added a new lock resumeMu and tracked the running state within the DAP server. resumeMu must be held in order to issue a debugger request that would start execution. This means it can be used to make sure that another goroutine does not resume execution while you are holding the lock.
Most of the synchronization logic is taken from PR #2530
Updates golang/vscode-go#123
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