[flang][flang-omp-report] Add flang-omp-report summarising script

The flang plugin ``flang-omp-report`` takes one fortran file in and returns a
YAML report file of the input file. This becomes an issue when you want to
analyse an entire project into one final report.
The purpose of this Python script is to generate a final YAML
report from all of the files generated by ``flang-omp-report``. The report can
have (currently) 2 formats; summary and log. Summary focuses on "summarizing"
all constructs and there clauses from all YAML files with a corresponding "count"
for each. Log instead combines the generated YAML files into one report in a
"cleaner" format. (Pseudo) Examples can be found for both formats at the top of
the script.

Differential Revision: https://reviews.llvm.org/D111042

Co-Authored by: Ivan Zhechev <ivan.zhechev@arm.com>