[x86/Linux] Do NOT use pXXX fields (dotnet/coreclr#9121)

[x86/Linux] Do NOT use pXXX fields (dotnet/coreclr#9121)

* [x86/Linux] Do NOT use pXXX fields

* Fix x86/Windows build error

* Fix another x86/Windows build error

* Fix typo

* Do NOT trash EBP

* Reflect the original semantics of EHContext::UpdateFrame

* Unify ReadXXX/LocateXXX into GetXXXLocation, and RestoreXXX/TrashXXX into SetXXXLocation

* Revert the order of pXXX fields

* Revise cgenx86.cpp

* Revert unnecessary changes

* Remove direct accesses to CALLEE_SAVED_REGISTERS_TAG

* Do NOT update pCurrentContext inside SetXXXLocation

* Update RegPtr via offset

* Unify REG_METHODS (and revise UpdateRegDisplay methods accordingly)

* Revise per feedback

* Fix x86/Windows build error

Commit migrated from https://github.com/dotnet/coreclr/commit/009c70f81d2899848ea254fd39969de91fd33519