[foozzie] Improve failure state deduplication

tools/foozzie/testdata/failure_output.txt

 #
 # V8 correctness failure
 # V8 correctness configs: x64,fullcode:x64,ignition_staging
 # V8 correctness sources: f602adcc
 # V8 correctness suppression: 
 #
 # CHECK
 #
 # Compared x64,fullcode with x64,ignition_staging
 #
 # Flags of x64,fullcode:
 --abort_on_stack_overflow --expose-gc --allow-natives-syntax --invoke-weak-callbacks --omit-quit --es-staging --random-seed 12345 --nocrankshaft --turbo-filter=~
 # Flags of x64,ignition_staging:
 --abort_on_stack_overflow --expose-gc --allow-natives-syntax --invoke-weak-callbacks --omit-quit --es-staging --random-seed 12345 --ignition-staging
 #
 # Difference:
 - unknown
 + not unknown
 #
 ### Start of configuration x64,fullcode:
 
 1
+v8-foozzie source: name/to/a/file.js
 2
+v8-foozzie source: name/to/file.js
   weird error
         ^
 3
 unknown
 
 
 ### End of configuration x64,fullcode
 #
 ### Start of configuration x64,ignition_staging:
 
 1
+v8-foozzie source: name/to/a/file.js
 2
+v8-foozzie source: name/to/file.js
   weird other error
 ^
 3
 not unknown
 
 
 ### End of configuration x64,ignition_staging