Feature proposal: Isolate test runs in terminal

[andyw8]

(I'm unsure how to best name this feature, so suggestions for a better title are welcome)

When trying out rust-analyzer, I noticed that running the tests via a Code Lens will 'take over' the terminal pane, e.g.

 *  Executing task: cargo test --package rust-by-example --bin rust-by-example -- tests::test_add --exact --show-output 

    Finished `test` profile [unoptimized + debuginfo] target(s) in 0.00s
     Running unittests src/main.rs (target/debug/deps/rust_by_example-60d877ca16f231b6)

running 1 test
test tests::test_add ... ok

successes:

successes:
    tests::test_add

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 1 filtered out; finished in 0.00s

 *  Terminal will be reused by tasks, press any key to close it. 

(Note the instruction on the final line).

This approach has the nice advantage that when you scroll back, you see only output for the last run of the test, rather than previous runs, making things less noisy.

It also prevent a user's typed command from getting mangled by the text sent to the terminal by the LSP.

(I've tagged this with vscode and server as I haven't yet looked at where it's implemented)

[vinistock]

Rust analyzer implements the test runs as VS Code tasks, which is what creates those new terminal panes with the "press any button to close".

I think the approach works well for Rust, but for Ruby I would be concerned that it could make it difficult to do terminal debugging. If it doesn't impact terminal debugging, then I think it should be fine to migrate.

We'd need to implement a proper task for run in terminal, which would essentially do what the current command already does. This is all on the VS Code side.