Handle symlinking edge cases

[withinboredom]

This one is interesting — though I’m not sure the best way to provide a test. I will have to look into maybe an integration test because it is a careful dance between how we resolve paths in the Caddy module vs. workers. I looked into making a proper change (literally using the same logic everywhere), but I think it is best to wait until #1646 is merged.

But anyway, this change deals with some interesting edge cases. I will use gherkin to describe them:

Feature: FrankenPHP symlinked edge cases
  Background: 
    Given a `test` folder
    And a `public` folder linked to `test`
    And a worker script located at `test/index.php`
    And a `test/nested` folder
    And a worker script located at `test/nested/index.php`
  Scenario: neighboring worker script
    Given frankenphp located in the test folder
    When I execute `frankenphp php-server --listen localhost:8080 -w index.php` from `public`
    Then I expect to see the worker script executed successfully
  Scenario: nested worker script
    Given frankenphp located in the test folder
    When I execute `frankenphp --listen localhost:8080 -w nested/index.php` from `public`
    Then I expect to see the worker script executed successfully
  Scenario: outside the symlinked folder
    Given frankenphp located in the root folder
    When I execute `frankenphp --listen localhost:8080 -w public/index.php` from the root folder
    Then I expect to see the worker script executed successfully
  Scenario: specified root directory
    Given frankenphp located in the root folder
    When I execute `frankenphp --listen localhost:8080 -w public/index.php -r public` from the root folder
    Then I expect to see the worker script executed successfully    

Trying to write that out in regular English would be more complex IMHO.

These scenarios should all pass now with this PR.

[henderkes]

do the edge cases only affect workers, not regular php requests?

[withinboredom]

@henderkes yes, only workers. I should have a nice test suite this weekend. Manually testing this is annoying.