[llvm] [CodeGen] Port WinEHPrepare to new pass manager (PR #74233)

[via llvm-commits]

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@@ -1206,15 +1220,12 @@ bool WinEHPrepare::prepareExplicitEH(Function &F) {
   LLVM_DEBUG(colorFunclets(F));
   LLVM_DEBUG(verifyPreparedFunclets(F));
 
-  BlockColors.clear();
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paperchalice wrote:

`BlockColors` and other members are moved into the wrapper pass `WinEHPrepareImpl`. `WinEHPrepare::runOnFunction` and `WinEHPreparePass::run` just create a local instance of `WinEHPrepareImpl`.

https://github.com/llvm/llvm-project/pull/74233