Add special named flag for invalid particles

[atmyers]

This lets you do

p.m_idcpu = LongParticleIDs::InvalidParticleID;

instead of

amrex::ParticleIDWrapper{p.m_idcpu} = -1;

The proposed changes:

• fix a bug or incorrect behavior in AMReX
• add new capabilities to AMReX
• changes answers in the test suite to more than roundoff level
• are likely to significantly affect the results of downstream AMReX users
• include documentation in the code and/or rst files, if appropriate

[atmyers]

Note that doing

p.m_idcpu *= -1;

is still okay, because if the original p.id() was positive, the new one will be negative, as long as the id is less than LongParticleIds::LastParticleID. Also, doing

p.m_idcpu *= -1;
p.m_idcpu *= -1;

will restore the original p.id() and p.cpu().