AbiSpecificInteger class Null safety

The supertype of all Abi-specific integer types.

Abi-specific integers should extend this class and annotate it with AbiSpecificIntegerMapping to declare the integer size and signedness for Abi.values.

For example:

/// The C `uintptr_t` type.
///
/// The [UintPtr] type is a native type, and should not be constructed in
/// Dart code.
/// It occurs only in native type signatures and as annotation on [Struct]
/// and [Union] fields.
@AbiSpecificIntegerMapping({
  Abi.androidArm: Uint32(),
  Abi.androidArm64: Uint64(),
  Abi.androidIA32: Uint32(),
  Abi.androidX64: Uint64(),
  Abi.fuchsiaArm64: Uint64(),
  Abi.fuchsiaX64: Uint64(),
  Abi.iosArm: Uint32(),
  Abi.iosArm64: Uint64(),
  Abi.linuxArm: Uint32(),
  Abi.linuxArm64: Uint64(),
  Abi.linuxIA32: Uint32(),
  Abi.linuxX64: Uint64(),
  Abi.linuxRiscv32: Uint32(),
  Abi.linuxRiscv64: Uint64(),
  Abi.macosArm64: Uint64(),
  Abi.macosX64: Uint64(),
  Abi.windowsIA32: Uint32(),
  Abi.windowsX64: Uint64(),
})
class UintPtr extends AbiSpecificInteger {
  const UintPtr();
}