Simplify readBitsIntBe() a bit

It's unnecessary to first left shift the mask to match the
relevant bits of value stored in "bits", because after the mask
is applied (`bits & mask`), this value will be shifted back right
anyway.

So it's easier to first shift "bits" to the right (and thus discard the
least significant bits of it, which are no longer part of the value
we want to read - but they remain in "bits" property for later fields,
note that we don't reassign it while shifting) and then AND with
the unchanged mask.

It saves one useless operation and reduces cognitive load - this way
is more straightforward.

Author: generalmimon

src/main/java/io/kaitai/struct/KaitaiStream.java

@@ -207,11 +207,9 @@ public long readBitsIntBe(int n) {
 
         // raw mask with required number of 1s, starting from lowest bit
         long mask = getMaskOnes(n);
-        // shift mask to align with highest bits available in "bits"
+        // shift "bits" to align the highest bits with the mask & derive the result
         int shiftBits = bitsLeft - n;
-        mask <<= shiftBits;
-        // derive reading result
-        long res = (bits & mask) >>> shiftBits;
+        long res = (bits >>> shiftBits) & mask;
         // clear top bits that we've just read => AND with 1s
         bitsLeft -= n;
         mask = getMaskOnes(bitsLeft);