using posix for join instead, gives us the proper / for file path separator (commontoolsinc#1807)

Author: ellyxir

packages/js-runtime/program.ts

@@ -1,6 +1,6 @@
 import { isDeno } from "@commontools/utils/env";
 import { ProgramResolver, Source } from "./interface.ts";
-import { dirname, join } from "@std/path";
+import { dirname, join } from "@std/path/posix";
 
 export class InMemoryProgram implements ProgramResolver {
   private modules: Record<string, string>;

packages/js-runtime/typescript/resolver.ts

@@ -1,6 +1,6 @@
 import ts from "typescript";
 import { Program, ProgramResolver, Source } from "../interface.ts";
-import { dirname, join } from "@std/path";
+import { dirname, join } from "@std/path/posix";
 
 export type UnresolvedModuleHandling =
   | { type: "allow"; identifiers: string[] }