Optimizing: Rename some members of `Location`.

Rename `RegisterLocation()` to `CoreRegister()` to include
the physical register type in the name while keeping the
name short. Rename similar functions for Fpu/Vec registers
and pairs to align with the new naming. Remove unnecessary
`Location::` qualifications within the class.

All changes outside of `locations.h` were done with
    sed '-res/::RegisterLocation\b/::CoreRegister/' \
        --in-place compiler/optimizing/*
    sed '-res/::FpuRegisterLocation\b/::FpuRegister/' \
        --in-place compiler/optimizing/*
    sed '-res/::RegisterPairLocation\b/::CoreRegisterPair/' \
        --in-place compiler/optimizing/*
    sed '-res/::FpuRegisterPairLocation\b/::FpuRegisterPair/' \
        --in-place compiler/optimizing/*
in the `art/` directory.

Test: testrunner.py -b --host-gtest --host --optimizing
Flag: EXEMPT PURE_REFACTOR
Change-Id: I0414ee0b4cfe15dc7f44c1ae4ee8c5273941b1c9