Remove constant duplication in jextract generated code

[ktoso]

Today we duplicate a lot of constants:

// TODO: rather than the C ones offer the Swift mappings
  public static final ValueLayout.OfBoolean C_BOOL = ValueLayout.JAVA_BOOLEAN;
  public static final ValueLayout.OfByte C_CHAR = ValueLayout.JAVA_BYTE;
  public static final ValueLayout.OfShort C_SHORT = ValueLayout.JAVA_SHORT;
  public static final ValueLayout.OfInt C_INT = ValueLayout.JAVA_INT;
  public static final ValueLayout.OfLong C_LONG_LONG = ValueLayout.JAVA_LONG;
  public static final ValueLayout.OfFloat C_FLOAT = ValueLayout.JAVA_FLOAT;
  public static final ValueLayout.OfDouble C_DOUBLE = ValueLayout.JAVA_DOUBLE;
  public static final AddressLayout C_POINTER = ValueLayout.ADDRESS
          .withTargetLayout(MemoryLayout.sequenceLayout(java.lang.Long.MAX_VALUE, ValueLayout.JAVA_BYTE));
  public static final ValueLayout.OfLong C_LONG = ValueLayout.JAVA_LONG;

in every generated file.

The origin of this was that initially we did not have SwiftKit, a shared library where we could put those constants on.

Now we do, so let's define them in swifkit somewhere and refer to them rather than duplicating them in every file that we generate