Fixes #63091

Continue Program was sending `singleThread: true` whenever the adapter
supported it, which caused some adapters to resume only the selected
thread. It now leaves `singleThread` unset and resumes all threads.

Adapters that support single-thread execution now show separate Continue
Program and Continue Thread buttons. Other adapters still show only
Continue Program.

<img width="247" height="108" alt="image"
src="https://github.com/user-attachments/assets/5059d291-4809-488b-9169-e4817852fb07"
/>

This change also:

- Updates thread states from the continue response instead of waiting
for a [continued event, which adapters are not expected to
send](https://github.com/microsoft/debug-adapter-protocol/blob/bf8a5d27e8040044b84b863f90916e08925ee811/debugAdapterProtocol.json#L243-L246).
- Treats an omitted allThreadsContinued in a continued event as true, as
required by the [DAP
specification](https://github.com/microsoft/debug-adapter-protocol/blob/main/debugAdapterProtocol.json#L260-L263).

Release Notes:

- Added a Continue Thread action and fixed Continue Program to resume
all threads.