minor #66367 [FrameworkBundle][HttpKernel] Skip resolving the runtime mode on web requests (nicolas-grekas)

This PR was merged into the 8.2 branch.

Discussion
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[FrameworkBundle][HttpKernel] Skip resolving the runtime mode on web requests

| Q             | A
| ------------- | ---
| Branch?       | 8.2
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Issues        | -
| License       | MIT

`DebugHandlersListener` needs `kernel.runtime_mode.web` only when a console event is dispatched, yet it's built on every request, and resolving that parameter takes 8 env var lookups, one of them throwing `EnvNotFoundException` when `APP_RUNTIME_MODE` isn't set. The listener now gets it as an env closure, which removes 8 of the 18 env lookups of a prod request on the Symfony Demo: about 50µs, -2.5% on its homepage redirect.

Needs #66366 on 8.1, so that `debug:container` can describe the new argument.

Commits
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f39a633c547 [FrameworkBundle][HttpKernel] Skip resolving the runtime mode on web requests