docs(typescript): add host configuration to rootDirs (#2401)

A `host` root directory is necessary for TypeScript to resolve imports for a tool executed at build time with `cfg = "host"`.

Arguably a similar change is also necessary for `cfg = "exec"`, however files would be in `bazel-out/k8-opt-exec-*/bin`, which can't be easily hard-coded in a tsconfig, so that's a problem to be tackled separately.

packages/typescript/internal/ts_project.bzl

@@ -388,6 +388,7 @@ def ts_project_macro(
     > "compilerOptions": {
     >     "rootDirs": [
     >         ".",
+    >         "../../bazel-out/host/bin/path/to",
     >         "../../bazel-out/darwin-fastbuild/bin/path/to",
     >         "../../bazel-out/k8-fastbuild/bin/path/to",
     >         "../../bazel-out/x64_windows-fastbuild/bin/path/to",