Introduce runtime_toolchain_type

According to discussions in #3854 having two toolchains of the same type for different things is troublesome. It's better to have separate runtime as well as compile toolchains.

This commit creates a new runtime_toolchain_type and registers toolchains without execution constraints for this type. Once merged, rules_ts can start consuming the new toolchain type in its js_binary rule to ensure the correct Node for the correct target environment is selected.

Fixed [Bug]: Execution toolchain defined without `target_compatible_with` makes it a candidate to selection

Fixes #3854
Work towards #3795

Author: guw

docs/Toolchains.md

@@ -3,6 +3,16 @@
 API docs for [Toolchain](https://docs.bazel.build/versions/main/toolchains.html) support.
 
 When you call `nodejs_register_toolchains()` in your `WORKSPACE` file it will setup a node toolchain for executing tools on all currently supported platforms.
+In `bzlmod` default toolchains are registered automatically when you depend on `rules_nodejs`.
+
+There are two toolchain types:
+
+1) The transpilation toolchain, which provides the Node runtime used to execute the transpiler (and type checker), as well as various helper tools and settings.
+   (`@rules_nodejs//nodejs:toolchain_type`)
+2) The Node runtime that executable Node outputs (e.g., js_binary) will run on.
+   (`@rules_nodejs//nodejs:runtime_toolchain_type`)
+
+See [//nodjes/BUILD.bazel](https://github.com/bazel-contrib/rules_nodejs/blob/main/nodejs/BUILD.bazel) for details.
 
 If you have an advanced use-case and want to use a version of node not supported by this repository, you can also register your own toolchains.
 
@@ -13,9 +23,9 @@ To run a custom toolchain (i.e., to run a node binary not supported by the built
 1) A rule which can build or load a node binary from your repository
    (a checked-in binary or a build using a relevant [`rules_foreign_cc` build rule](https://bazelbuild.github.io/rules_foreign_cc/) will do nicely).
 2) A [`nodejs_toolchain` rule](Core.html#nodejs_toolchain) which depends on your binary defined in step 1 as its `node`.
-3) A [`toolchain` rule](https://bazel.build/reference/be/platform#toolchain) that depends on your `nodejs_toolchain` rule defined in step 2 as its `toolchain`
-   and on `@rules_nodejs//nodejs:toolchain_type` as its `toolchain_type`. Make sure to define appropriate platform restrictions as described in the
-   documentation for the `toolchain` rule.
+3) Two [`toolchain` rules](https://bazel.build/reference/be/platform#toolchain) each depends on your `nodejs_toolchain` rule defined in step 2 as its `toolchain`
+   and one on `@rules_nodejs//nodejs:toolchain_type` as its `toolchain_type` and the other one  `@rules_nodejs//nodejs:runtime_toolchain_type`.
+   Make sure to define appropriate platform restrictions as described in the documentation for the `toolchain` rule.
 4) A call to [the `register_toolchains` function](https://bazel.build/rules/lib/globals#register_toolchains) in your `WORKSPACE`
    that refers to the `toolchain` rule defined in step 3.