Move DFG::OSRExitCompiler methods into DFG::OSRExit [step 1].

Move DFG::OSRExitCompiler methods into DFG::OSRExit [step 1].
https://bugs.webkit.org/show_bug.cgi?id=175208
<rdar://problem/33732402>

Reviewed by Saam Barati.

This will minimize the code diff and make it easier to review the patch for
https://bugs.webkit.org/show_bug.cgi?id=175144 later.  We'll do this patch in 3
steps:

1. Do the code changes to move methods into OSRExit.
2. Copy the 64-bit and common methods into DFGOSRExit.cpp, and delete the unused DFGOSRExitCompiler files.
3. Merge the 32-bit OSRExitCompiler methods into the 64-bit version, and delete DFGOSRExitCompiler32_64.cpp.

Splitting this refactoring into these 3 steps also makes it easier to review this
patch and understand what is being changed.

* dfg/DFGOSRExit.h:
* dfg/DFGOSRExitCompiler.cpp:
(JSC::DFG::OSRExit::emitRestoreArguments):
(JSC::DFG::OSRExit::compileOSRExit):
(JSC::DFG::OSRExitCompiler::emitRestoreArguments): Deleted.
(): Deleted.
* dfg/DFGOSRExitCompiler.h:
(JSC::DFG::OSRExitCompiler::OSRExitCompiler): Deleted.
(): Deleted.
* dfg/DFGOSRExitCompiler32_64.cpp:
(JSC::DFG::OSRExit::compileExit):
(JSC::DFG::OSRExitCompiler::compileExit): Deleted.
* dfg/DFGOSRExitCompiler64.cpp:
(JSC::DFG::OSRExit::compileExit):
(JSC::DFG::OSRExitCompiler::compileExit): Deleted.
* dfg/DFGThunks.cpp:
(JSC::DFG::osrExitGenerationThunkGenerator):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@220298 268f45cc-cd09-0410-ab3c-d52691b4dbfc