Shorten SelectFields constructor using array unpacking

[kylekatarnls]

Summary

Syntax proposal: usage of array unpacking

Benefits:

• Avoid intermediate variable
• Avoid magic numbers 0 and 1
• Avoid ambiguous 'fields' name: fields[0] (which make think the first field only goes to select and the second one to relations while it's actually 2 groups of different things that have been retrieved and the unit is not the field)
• Solve a PHPStan error

Type of change

Misc. change (syntax)

[mfn]

Thank you @kylekatarnls !