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