Merge #4448

4448: Generate configuration for launch.json r=vsrs a=vsrs

This PR adds two new commands: `"rust-analyzer.debug"` and `"rust-analyzer.newDebugConfig"`. The former is a supplement to the existing `"rust-analyzer.run"` command and works the same way: asks for a runnable and starts new debug session. The latter allows adding a new configuration to **launch.json** (or to update an existing one).

If the new option `"rust-analyzer.debug.useLaunchJson"` is set to true then `"rust-analyzer.debug"` and Debug Lens will first look for existing debug configuration in **launch.json**. That is, it has become possible to specify startup arguments, env variables, etc.

`"rust-analyzer.debug.useLaunchJson"` is false by default, but it might be worth making true the default value. Personally I prefer true, but I'm not sure if it is good for all value.

----
I think that this PR also solves https://github.com/rust-analyzer/rust-analyzer/issues/3441.
Both methods to update launch.json mentioned in the issue do not work:
1. Menu. It is only possible to add a launch.json configuration template via a debug adapter. And anyway it's only a template and it is impossible to specify arguments from an extension.

2. DebugConfigurationProvider. The exact opposite situation: it is possible to specify all debug session settings, but it is impossible to export these settings to launch.json.

Separate `"rust-analyzer.newDebugConfig"` command looks better for me.

----
Fixes #4450
Fixes #3441

Co-authored-by: vsrs <vit@conrlab.com>
Co-authored-by: vsrs <62505555+vsrs@users.noreply.github.com>

crates/rust-analyzer/src/main_loop/handlers.rs

@@ -1011,6 +1011,7 @@ fn to_lsp_runnable(
     runnable: Runnable,
 ) -> Result<lsp_ext::Runnable> {
     let spec = CargoTargetSpec::for_file(world, file_id)?;
+    let target = spec.as_ref().map(|s| s.target.clone());
     let (args, extra_args) = CargoTargetSpec::runnable_args(spec, &runnable.kind)?;
     let line_index = world.analysis().file_line_index(file_id)?;
     let label = match &runnable.kind {
@@ -1018,7 +1019,9 @@ fn to_lsp_runnable(
         RunnableKind::TestMod { path } => format!("test-mod {}", path),
         RunnableKind::Bench { test_id } => format!("bench {}", test_id),
         RunnableKind::DocTest { test_id, .. } => format!("doctest {}", test_id),
-        RunnableKind::Bin => "run binary".to_string(),
+        RunnableKind::Bin => {
+            target.map_or_else(|| "run binary".to_string(), |t| format!("run {}", t))
+        }
     };
     Ok(lsp_ext::Runnable {
         range: to_proto::range(&line_index, runnable.range),