[windows] R is now found if several binaries in PATH

This solves issue with some R intallation where several R version are on PATH but not in registry, e.g egde case with scoop.

WHERE command on CMD will return full path to each file found, and not only one command like which on UNIX

Author: cderv

src/core/path.ts

@@ -95,7 +95,10 @@ export async function which(cmd: string) {
     { cmd: args, stderr: "piped", stdout: "piped" },
   );
   if (result.code === 0) {
-    return result.stdout?.trim();
+    return Deno.build.os === "windows"
+      // WHERE return all files found, only first is kept
+      ? result.stdout?.split("\n")[0].trim()
+      : result.stdout?.trim();
   } else {
     return undefined;
   }