Fix BigInteger bitwise operators on certain negative numbers

[Rob-Hague]

Fixes#109669 c.f. #109669 (comment)

[Rob-Hague]

An alternative or follow-up could be to remove this constructor and replace the 3 uses with calls to the public ROS<byte> constructor, e.g.

diff --git a/src/libraries/System.Runtime.Numerics/src/System/Numerics/BigInteger.cs b/src/libraries/System.Runtime.Numerics/src/System/Numerics/BigInteger.cs
index b3355ff6867..4a0d53e6be2 100644
--- a/src/libraries/System.Runtime.Numerics/src/System/Numerics/BigInteger.cs+++ b/src/libraries/System.Runtime.Numerics/src/System/Numerics/BigInteger.cs@@ -2476,7 +2476,7 @@ private static BigInteger Subtract(ReadOnlySpan<uint> leftBits, int leftSign, Re
if (rightBufferFromPool != null)
ArrayPool<uint>.Shared.Return(rightBufferFromPool);
- var result = new BigInteger(z);+ var result = new BigInteger(MemoryMarshal.AsBytes(z));
if (resultBufferFromPool != null)
ArrayPool<uint>.Shared.Return(resultBufferFromPool);

[huoyaoyuan]

Duplicate of#105456

[tannergooding]

Merged #105456

Will still take this PR for the explicit regression test and typo fix.

[jeffhandley]

@tannergooding Once this is merged, do you want to cherry-pick it into #109732 for the backport too so we take this new test with the fix?

[tannergooding]

Can do.