Add options to dump PGO counts in text.
Added text options to -pgo-view-counts and -pgo-view-raw-counts that dump block frequency and branch probability info in text.
This is useful when the graph is very large and complex (the dot command crashes, lines/edges too close to tell apart, hard to navigate without textual search) or simply when text is preferred.
Reviewed By: davidxl
Differential Revision: https://reviews.llvm.org/D37776