Runnable env

[vsrs]

This PR adds on option to specify (in the settings.json) environment variables passed to the runnable.
The simplest way for all runnables in a bunch:

    "rust-analyzer.runnableEnv": {
        "RUN_SLOW_TESTS": "1"
    }

Or it is possible to specify vars more granularly:

    "rust-analyzer.runnableEnv": [
        {
            // "mask": null, // null mask means that this rule will be applied for all runnables
            env: {
                 "APP_ID": "1",
                 "APP_DATA": "asdf"
            }
        },
        {
            "mask": "test_name",
            "env": {
                 "APP_ID": "2", // overwrites only APP_ID
            }
        }
    ]

You can use any valid RegExp as a mask. Also note that a full runnable name is something like run bin_or_example_name, test some::mod::test_name or test-mod some::mod, so it is possible to distinguish binaries, single tests, and test modules with this masks: "^run", "^test " (the trailing space matters!), and "^test-mod" respectively.

Fixes #4450

I suppose this info should be somewhere in the docs, but unsure where is the best place.

[matklad]

I suppose this info should be somewhere in the docs, but unsure where is the best place.

I think we need top-level section in manual.adoc for this:

== Editor Features
==== VS Code

[vsrs]

@matklad I added the doc section.

[matklad]

bors r+

[bors]

Build succeeded:

• Rust (ubuntu-latest)
• Rust (windows-latest)
• Rust (macos-latest)
• TypeScript (ubuntu-latest)
• TypeScript (windows-latest)
• TypeScript (macos-latest)

[adaszko]

Are those environment variables also applied when clicking the "Debug" code lens over a unit test in VSCode?

[vsrs]

Yes, they are.