Rename our_snprintf to d_r_snprintf per the new global variable naming policy. Rename our_*sscanf to d_r_*sscanf.
Rename DR's internal string routines to use a d_r_ prefix to reduce name conflicts with static linking. Because on Windows we still want to use the standard names (because we import from ntdll), we resort to macro renames within core/ just like we're doing with snprintf.
Remove includes of string.h in core/ to avoid macros and inlined functions pulling in libc functions, now that our versions use different names.
Issue: #3348