Improve accuracy of complex and real acosh

[pearu]

• Improve the accuracy of complex acosh as follows (complex64):

                       current main  -> this PR
  ULP difference == 0 count is 141180  -> 839342
  ULP difference == 1 count is 10145   -> 162239
  ULP difference == 2 count is 1929    -> 420
  ULP difference == 3 count is 826     -> 0
  ULP difference >= 4 count is 847921  -> 0

• Improve the accuracy of real acosh as follows (float32):

                         current main  -> this PR
  ULP difference == 0 count is 966912    -> 993686
  ULP difference == 1 count is 33008     -> 6303
  ULP difference == 2 count is 49        -> 12
  ULP difference == 3 count is 13        -> 0
  ULP difference >= 4 count is 19        -> 0

This PR is created on top of https://github.com/openxla/stablehlo/pull/2409