Add HTTP/2 Empty CONTINUATION & DATA frame counter

[maskit]

[maskit]

[approve ci autest]

[maskit]

I updated the documentation.

[maskit]

Strange error on FreeBSD build

/usr/bin/c++  -pthread CMakeFiles/test_vars.dir/print_funcs.cc.o CMakeFiles/test_vars.dir/vars_test.cc.o -o test_vars  -Wl,-rpath,/usr/home/jenkins/workspace/Github_Builds/freebsd/src/build/lib/swoc libesitest.a ../common/libesi-common.a ../lib/libesicore.a ../fetcher/libfetcher.a ../common/libesi-common.a /usr/lib/libz.so ../../../lib/swoc/libswoc-1.5.12.so 
ld: error: vars_test.cc:(function std::__1::vector<Catch::TestCaseTracking::ITracker*, std::__1::allocator<Catch::TestCaseTracking::ITracker*> >::__recommend(unsigned long) const: .text._ZNKSt3__16vectorIPN5Catch16TestCaseTracking8ITrackerENS_9allocatorIS4_EEE11__recommendEm+0x3D): relocation R_X86_64_PLT32 out of range: -288230376151713297 is not in [-2147483648, 2147483647]; references std::__1::vector<Catch::TestCaseTracking::ITracker*, std::__1::allocator<Catch::TestCaseTracking::ITracker*> >::capacity() const
>>> defined in CMakeFiles/test_vars.dir/vars_test.cc.o
c++: error: linker command failed with exit code 1 (use -v to see invocation)

[maskit]

[approve ci freebsd]

[bneradt]

Thanks for the review updates. Looks good.

[cmcfarlen]

Cherry-picked to v10.0.x