src: check if the script file exists before starting inspector

[cola119]

Fixed #42600

Currently node --inspect-brk index.js will start the inspector and wait a connection event though index.js doesn't exist. And immediately after connected, node will throw Cannot find module error and wait to be disconnected.

This PR added the ability to check for the existence of the script file before an inspector agent is started. If the script is missing, inspector is not enabled and node module loader will throw MODULE_NOT_FUOND error.

	v17.9.0	This PR
node --inspect no-exist.js	Enable inspector agent & MODULE_NOT_FOUND error	MODULE_NOT_FOUND error
node --inspect-brk no-exist.js	Enable inspector agent	MODULE_NOT_FOUND error
node inspect no-exist.js	Enable inspector agent but commands fail	MODULE_NOT_FOUND error in a child process
node --inspect	Enable inspector agent	Enable inspector agent
node --inspect-brk	Enable inspector agent	Enable inspector agent

[nodejs-github-bot]

Review requested:

• @nodejs/startup

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/44081/

[legendecas]

Agent::PauseOnNextJavascriptStatement assumes that the inspector agent is started with Agent::Start and Agent::client_ exists. Early break from Environment::InitializeInspector and not calling Agent::Start can break the assumption that if the process is started with --inspect-brk the agent must have been started.

Like say, we can crash the process with segment fault with the following setup:

// preload.js
require('fs').writeFileSync('./main.js', 'console.log("main")', 'utf8);

and run node with node --inspect-brk --require=./preload.js main.js with main.js not existing.

Maybe we can instead delay the wait for client connection to the time before we pause on next javascript statement?

[legendecas]

Nit: can we assert that this statement is not present in the output?