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>

1 files changed, 7 insertions, 0 deletions

diff --git a/tests/specs/run/exit_code/main.js b/tests/specs/run/exit_code/main.js
new file mode 100644
index 000000000..1ba1f06c4
--- /dev/null
+++ b/tests/specs/run/exit_code/main.js
@@ -0,0 +1,7 @@
+if (Deno.exitCode != 0) {
+  throw new Error("boom!");
+}
+
+Deno.exitCode = 42;
+
+console.log("Deno.exitCode", Deno.exitCode);