Fix spelling errors

Most errors found with:

codespell -L cach,thst,odly,aslo,parm,parms,inpu,ges,prset,pevent,ptd,pring,valu,noo,noe,ned,inout,ro,siz,froms,nd,fo,singl,sart,multy,tthe,allong,ment,inate,nodel,tring,alse,ture,thi,wille,numer

Some more manually found (its -> it's)

c++20: Do not use apostrophe (e.g. can't) in unquoted #error message

modules/libcom/test/epicsThreadPerform.cpp

@@ -119,7 +119,7 @@ static void threadSleepQuantumTest ()
             "The epicsThreadSleepQuantum() call returns %f sec.\n",
                 quantum );
         printf (
-            "This doesnt match the quantum estimate "
+            "This doesn't match the quantum estimate "
             "of %f sec within %s.\n",
                 quantumEstimate, pTol );
     }