[GR-65172] Insert load and store conversions for unsafe accesses during PEA.

[graalvmbot]

The example below should return 0xFFFFFFF0, because byte accesses are sign extended, which is also done in
DefaultLoweringProvider.java.
PEA though just extracts the constant and returns it, so we get 0xF0F0F0F0, which is incorrect.

static class Data {
    int value = 0xF0F0F0F0;
}
public static int getByte() {
      Data data = new Data();
      return Unsafe.getUnsafe().getByte(data, 12);
}

The PR fixes this issue by inserting load and store conversions during PEA and also adds test cases.