Fix spill check for struct lclVars (dotnet/coreclr#23570)

Fix spill check for struct lclVars (dotnet/coreclr#23570)

* Fix spill check for struct lclVars

With the 1st class struct changes, the `SPILL_APPEND` check for the case of an assignment to a lclVar needs to handle block ops as well as lclVar lhs.

Fix dotnet/coreclr#23545

Commit migrated from https://github.com/dotnet/coreclr/commit/f036d2339b030258bf31bc73ebc23f553744fa04