Allow more Bignum primitives to inline (#20361)

Sylvain Henryrequested to merge
hsyl20/ghc:hsyl20/bignum-inline2 into master

See #20361 for the plan. In this batch:

  • add constant folding for bigNatCompareWord#
  • allow Integer Eq/Ne/Gt/Ge/Lt/Le/Compare to inline
  • allow Integer signum to inline

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