Dependency Injection: fix custom loader on Windows

[jrfnl]

Context

• Fixed Dependency Injection Compile command on Windows

Summary

This PR can be summarized in the following changelog entry:

• Fixed Dependency Injection Compile command on Windows

Relevant technical choices:

Compile-DI: fix custom loader on Windows

Both the returned value from glob as well as the classmap generated by Composer contain file paths with a mix of forward and backward slashes when run on Windows.

This was breaking the compile-di command.

Previously it was silently broken - it wouldn't work, but without throwing an error.
Since the addition of the Schema_Blocks it would fail with an exception.

This commit fixes this by:

1. Adding a normalize_slashes() method.
2. Calling that method in the relevant places in the script to make sure that paths are normalized before they are compared based on their string value.

Custom_Loader::getClassFromClassMap(): efficiency fix

The Custom_Loader::getClassFromClassMap() would do a loop through all classes registered in the classmap via a foreach for each class requested (which could be many).

By flipping the array and using isset() instead, the functionality remains the same, but is infinitely faster.

Test instructions

Test instructions for the acceptance test before the PR gets merged

This PR can be acceptance tested by following these steps:

This should be tested on the three OS-es used by devs: Linux, MacOS and Windows.

• On trunk, run composer install.
  On Linux and Mac this should be successful already, on Windows it will fail with an exception during the compile-di step.
• After running the command, verify that the src/generated folder contains both the container.php and the container.php.meta file and that those are not empty.
• Switch to this branch, rinse & repeat.
  If all is good, the command should now finish successfully on all three OSes.

[afercia]

CR 👍
Acceptance: tested on macOS and Windows 👍
Will ask a Linuxer to test.

Note: on Windows, the build fails for an unrelated, new, error on the task grunt shell:install-schema-blocks. Will check if it's a known issue or create a new one. (Note: happens also on trunk)

[afercia]

@enricobattocchi was so kind to test on his Linux machine: composer install works as expected.
Acceptance 👍 Merging!

[increddibelly]

works great on windows 👍