Fix deprecations triggered from code called by native code

[stof]

The debug backtrace does not provide the file key for frames that are not happening in a file, like eval'd code.

Fixes #44

[stof]

The more precise type for the $backtrace argument is taken from the return types in the phpstan source code (as this is the tool having the right one). With that, psalm at the existing level 2 and phpstan at level 7 (we are currently at level 6) are detecting the issues in the delegateTriggerToBackend method that are fixed here. phpstan at level 7 is also able to detect the broken usages in triggerIfCalledFromOutside.
And this also brings us closer to reaching the max level of both tools (actually, with this PR and #52, the phpstan max level only reports false positives)

[greg0ire]

Is it possible to come up with a test for this?

[stof]

I will try to write a test using eval.

[stof]

@greg0ire we now have a test