Determine ProjectSettings' resource path early

[RandomShaper]

Consider the following sequence:

• On some platform Godot tries to find the relevant PCK.
• One of the attempts is for executable_path.pck.
• FileAccess does fix_path(), which for ACCESS_FILESYSTEM calls ProjectSettings::get_singleton()->get_resource_path().
• Such resource path hasn't been already set so early.
• Therefore, in that platform, in which every real file system path must be prefixed will receive an invalid path on FileAccess::open().

This PR fixes that pathological case by just letting ProjectSettings fill the resource path value earlier.

Separate PR submitted for 3.x: #64926.

[akien-mga]

Thanks!