Rename constants to make their names more consistent with each other.
All header constants start now by HEADER_ and all Bandwidth Lines by
BWLINE_.
The constants that are a list of keys are now named KEYS instead of
KEY_VALUE or KEY_VALUE.

These are the substitutions made:

s/BW_KEYVALUE_SEP_V1/BWLINE_KEYVALUES_SEP_V1/
s/BW_KEYVALUES_BASIC/BWLINE_KEYS_V0/
s/BW_KEYVALUES_FILE/BWLINE_KEYS_V1_1/
s/BW_KEYVALUES_EXTRA_BWS/BWLINE_KEYS_V1_2/
s/BANDWIDTH_LINE_KEY_VALUES_MONITOR/BWLINE_KEYS_V1_4/
s/BW_KEYVALUES_EXTRA/BWLINE_KEYS_V1/
s/BW_KEYVALUES_INT/BWLINE_INT_KEYS/
s/BW_KEYVALUES/BWLINE_ALL_KEYS/
s/EXTRA_ARG_KEYVALUES/HEADER_KEYS_V1X/
s/STATS_KEYVALUES/HEADER_KEYS_V1_2/
s/BW_HEADER_KEYVALUES_RECENT_MEASUREMENTS_EXCLUDED/HEADER_RECENT_MEASUREMENTS_EXCLUDED_KEYS/
s/BW_HEADER_KEYVALUES_MONITOR/HEADER_KEYS_V1_4/
s/BANDWIDTH_HEADER_KEY_VALUES_INIT/HEADER_INIT_KEYS/
s/KEYVALUES_INT/HEADER_INT_KEYS/
s/UNORDERED_KEYVALUES/HEADER_UNORDERED_KEYS/
s/ALL_KEYVALUES/HEADER_ALL_KEYS/

Part of #30196