RFR: 8332697: ubsan: shenandoahSimpleBitMap.inline.hpp:68:23: runtime error: signed integer overflow: -9223372036854775808 - 1 cannot be represented in type 'long int'

[William Kemper]

Use an unsigned version of `right_n_bits`.

-------------

Commit messages:
 - Use an unsigned variant of right_n_bits

Changes: https://git.openjdk.org/jdk/pull/21236/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21236&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8332697
  Stats: 5 lines in 1 file changed: 3 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/21236.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21236/head:pull/21236

PR: https://git.openjdk.org/jdk/pull/21236