Move blob handling into StgToCmm
Move handling of big literal strings from CmmToAsm to StgToCmm.
It avoids the use of sdocWithDynFlags
(cf #10143 (closed)). We might need to move
this handling even higher in the pipeline in the future (cf #17960):
this patch will make it easier.
Also fix T16190 test (which tests big literal strings) which was using collect_stats
instead of collect_compiler_stats