[clang] [clang-repl] Always clean up scope and context for TopLevelStmtDecl (PR #150215)

[via cfe-commits]

devajithvs wrote:

CC: @weliveindetail, @vgvassilev 

Not sure `fail.cpp` is the best place for this test to go as this can be a bit confusing
`cat %s | not clang-repl -Xcc -Xclang -Xcc -verify | FileCheck %s`
is expected to pass as `-verify` is expected to fail. But the test itself will fail if it hits an assertion.

Fixes one of the failing test when updating ROOT/CLING to LLVM20: https://github.com/root-project/root/pull/19242

https://github.com/llvm/llvm-project/pull/150215