feat: Add Deno.exitCode API (#23609)

This commits adds the ability to set a would-be exit code 
for the Deno process without forcing an immediate exit, 
through the new `Deno.exitCode` API.

- **Implements `Deno.exitCode` getter and setter**: Adds support for
setting
and retrieving a would-be exit code via `Deno.exitCode`.
This allows for asynchronous cleanup before process termination 
without immediately exiting.
- **Ensures type safety**: The setter for `Deno.exitCode` validates that
the provided value is a number, throwing a TypeError if not, to ensure
that
only valid exit codes are set.

Closes to #23605

---------

Co-authored-by: Bartek Iwańczuk <biwanczuk@gmail.com>

tests/unit_node/process_test.ts

@@ -787,10 +787,10 @@ Deno.test("process.exitCode", () => {
   assertEquals(process.exitCode, undefined);
   process.exitCode = 127;
   assertEquals(process.exitCode, 127);
-  // deno-lint-ignore no-explicit-any
-  (process.exitCode as any) = "asdf";
-  // deno-lint-ignore no-explicit-any
-  assertEquals(process.exitCode as any, "asdf");
+  assertThrows(() => {
+    // deno-lint-ignore no-explicit-any
+    (process.exitCode as any) = "asdf";
+  });
   // deno-lint-ignore no-explicit-any
   (process.exitCode as any) = "10";
   process.exitCode = undefined; // reset
@@ -827,7 +827,7 @@ Deno.test("process.exitCode in should change exit code", async () => {
   );
   await exitCodeTest(
     "import process from 'node:process'; process.exitCode = NaN;",
-    0,
+    1,
   );
 });