The immediate goal is to start producing an HTML report to debug and explain
include-cleaner recommendations.
For now, this includes only the lowest-level piece: a list of the references
found in the source code.
How this fits into future ideas:
- under refs we can also show the headers providing the symbol, which includes
match those headers etc
- we can also annotate the #include lines with which symbols they cover, and
add whichever includes we're suggesting too
- the include-cleaner tool will likely have modes where it emits diagnostics
and/or applies edits, so the HTML report is behind a flag
Differential Revision: https://reviews.llvm.org/D135956