Add warning type into TopDirs and TopFiles index

* The index was a directory or file path.
  This change adds additional entries that have
  warning type prefix in the index.
* In the "Directories/Files with at least 1% warnings"
  section, the list will include number of warnings for
  (1) "all warnings in a directory/file"
  (2) "warnings of a type in a directory/file"
  (3) "warnings of a type in all directories/files"
  Examples:
    4273 (8.7%) frameworks/av/...
    4130 (8.4%) packages/...
    2427 (5.0%) [google-explicit-constructor] */...
    1628 (3.3%) [cert-err34-c] */...
    1099 (2.2%) [google-runtime-int] bionic/tests/math_data/...
     608 (1.2%) [cert-err34-c] external/...

Bug: 231245501
Test: warn.py --url=http://cs/android --separator='?l=' build.log > warnings.html
Test: warn.py --gencsv build.log > warnings.csv
Change-Id: I13bb54c846ad514334f78c5a71e994a131a92963