Review merge of branch 'hrtf_binary' into 'main'

While cleaning up, I've stumbed across a number of questions with the merge of the branch 'hrtf_binary' into 'main', see also 6b1025dc

1. lib_com/options.h - a lot of cleaned-out preprocessor macros were added agin, probably as a result of a wrongly resolved merge request <-- this is not a problem, I will take care of resolving this when cleaning up the new switches
2. lib_dec/ivas_corecoder_dec_reconfig.c - code within SBA_BR_SWITCHING_RECONFIG was removed, reason unclear <-- seems this was resolved in !413 (comment 10694)
3. lib_rend/ivas_binauralRenderer.c - changes within HRTF_BINARY_FILE seem to be missing in the code portions wrapped by FIX_FIX_I59, probably a merge issue
4. .gitignore - the directory 'Externals' was added; unclear, what this belongs to