Import mpdecimal-4.0.0 Third-Party Import of: https://www.bytereef.org/mpdecimal/ Request Document: go/android3p For CL Reviewers: go/android3p#reviewing-a-cl For Build Team: go/ab-third-party-imports Bug: http://b/390479029 Security Questionnaire: http://b/390479029#comment1 Test: m libmpdec Change-Id: I274650578c996fc7ccf454d1d3a913714d10ac4b