Model the length of open arrays as `NativeInt` under Delphi 12

[cirras]

Prerequisites

• This improvement has not already been suggested.
• This improvement would be generally useful, not specific to my code or setup.

Engine area

Delphi language support

Improvement description

The following intrinsics should return NativeInt for an open array type under Delphi 12:

• Length
• High
• Low

Rationale

The hidden "high bound" parameter type for an open array parameter was changed from Integer to NativeInt, an alias of Integer or Int64, depending on the target CPU. This means that Length, High, and Low for open array parameters in 64-bit compilers now return 64-bit value.

See: https://docwiki.embarcadero.com/RADStudio/Athens/en/What%27s_New#Quality_Improvements