Fix constant simplifying in dsolve
Fix constant simplifying in dsolve

+ Fixes constant-collision errors in dsolve for good
+ Constant numbering starts with C1, unless specified otherwise
+ Specific checks for common subexpression and linear simplifications

yashsharan/sympy,bukzor/sympy,beni55/sympy,Shaswat27/sympy,mcdaniel67/sympy,jamesblunt/sympy,aktech/sympy,liangjiaxing/sympy,moble/sympy,drufat/sympy,jbbskinny/sympy,Mitchkoens/sympy,shikil/sympy,sampadsaha5/sympy,Davidjohnwilson/sympy,liangjiaxing/sympy,cccfran/sympy,farhaanbukhsh/sympy,ChristinaZografou/sympy,sunny94/temp,maniteja123/sympy,atsao72/sympy,vipulroxx/sympy,abhiii5459/sympy,wanglongqi/sympy,AkademieOlympia/sympy,sunny94/temp,wanglongqi/sympy,diofant/diofant,Designist/sympy,postvakje/sympy,grevutiu-gabriel/sympy,emon10005/sympy,mafiya69/sympy,shipci/sympy,chaffra/sympy,postvakje/sympy,wanglongqi/sympy,cccfran/sympy,Curious72/sympy,jamesblunt/sympy,emon10005/sympy,hargup/sympy,kevalds51/sympy,meghana1995/sympy,yashsharan/sympy,drufat/sympy,ga7g08/sympy,iamutkarshtiwari/sympy,kaichogami/sympy,dqnykamp/sympy,yashsharan/sympy,beni55/sympy,shipci/sympy,jaimahajan1997/sympy,Sumith1896/sympy,rahuldan/sympy,abloomston/sympy,toolforger/sympy,jerli/sympy,MridulS/sympy,ChristinaZografou/sympy,madan96/sympy,wyom/sympy,debugger22/sympy,Mitchkoens/sympy,skirpichev/omg,Mitchkoens/sympy,cswiercz/sympy,aktech/sympy,asm666/sympy,AunShiLord/sympy,ahhda/sympy,asm666/sympy,pandeyadarsh/sympy,pbrady/sympy,emon10005/sympy,saurabhjn76/sympy,mafiya69/sympy,Davidjohnwilson/sympy,hargup/sympy,shipci/sympy,Gadal/sympy,meghana1995/sympy,Titan-C/sympy,mcdaniel67/sympy,souravsingh/sympy,garvitr/sympy,grevutiu-gabriel/sympy,saurabhjn76/sympy,VaibhavAgarwalVA/sympy,debugger22/sympy,Shaswat27/sympy,beni55/sympy,aktech/sympy,abhiii5459/sympy,Designist/sympy,rahuldan/sympy,sampadsaha5/sympy,garvitr/sympy,cccfran/sympy,toolforger/sympy,toolforger/sympy,Sumith1896/sympy,drufat/sympy,chaffra/sympy,maniteja123/sympy,farhaanbukhsh/sympy,jerli/sympy,Curious72/sympy,lindsayad/sympy,Arafatk/sympy,jbbskinny/sympy,kumarkrishna/sympy,lindsayad/sympy,cswiercz/sympy,ChristinaZografou/sympy,vipulroxx/sympy,moble/sympy,Gadal/sympy,abhiii5459/sympy,sahmed95/sympy,garvitr/sympy,yukoba/sympy,Vishluck/sympy,jaimahajan1997/sympy,Titan-C/sympy,MridulS/sympy,madan96/sympy,MridulS/sympy,atreyv/sympy,skidzo/sympy,Gadal/sympy,ga7g08/sympy,mcdaniel67/sympy,iamutkarshtiwari/sympy,mafiya69/sympy,Vishluck/sympy,oliverlee/sympy,lindsayad/sympy,souravsingh/sympy,bukzor/sympy,kaichogami/sympy,VaibhavAgarwalVA/sympy,sunny94/temp,moble/sympy,kaichogami/sympy,shikil/sympy,asm666/sympy,Vishluck/sympy,hargup/sympy,kumarkrishna/sympy,AunShiLord/sympy,iamutkarshtiwari/sympy,kevalds51/sympy,ahhda/sympy,madan96/sympy,ahhda/sympy,farhaanbukhsh/sympy,sahmed95/sympy,souravsingh/sympy,skidzo/sympy,ga7g08/sympy,sampadsaha5/sympy,pbrady/sympy,AkademieOlympia/sympy,wyom/sympy,atreyv/sympy,wyom/sympy,VaibhavAgarwalVA/sympy,rahuldan/sympy,AunShiLord/sympy,grevutiu-gabriel/sympy,kumarkrishna/sympy,Curious72/sympy,maniteja123/sympy,Davidjohnwilson/sympy,jamesblunt/sympy,kevalds51/sympy,kaushik94/sympy,sahilshekhawat/sympy,MechCoder/sympy,oliverlee/sympy,debugger22/sympy,shikil/sympy,jaimahajan1997/sympy,jbbskinny/sympy,Sumith1896/sympy,sahilshekhawat/sympy,sahilshekhawat/sympy,yukoba/sympy,kaushik94/sympy,pandeyadarsh/sympy,Designist/sympy,kaushik94/sympy,abloomston/sympy,chaffra/sympy,vipulroxx/sympy,jerli/sympy,yukoba/sympy,atreyv/sympy,atsao72/sympy,abloomston/sympy,Titan-C/sympy,postvakje/sympy,oliverlee/sympy,sahmed95/sympy,pandeyadarsh/sympy,MechCoder/sympy,liangjiaxing/sympy,skidzo/sympy,dqnykamp/sympy,MechCoder/sympy,meghana1995/sympy,bukzor/sympy,cswiercz/sympy,Arafatk/sympy,Shaswat27/sympy,atsao72/sympy,dqnykamp/sympy,AkademieOlympia/sympy,pbrady/sympy,saurabhjn76/sympy,Arafatk/sympy