[clang] [clang-repl] Expose CreateExecutor() and ResetExecutor() in extended Interpreter interface (PR #84460)

[Stefan Gränitz via cfe-commits]

weliveindetail wrote:

Build bot https://lab.llvm.org/buildbot/#/builders/196/builds/46799 detected an issue with the test -- I will try and push a fix quickly:
```
tools/clang/unittests/Interpreter/CMakeFiles/ClangReplInterpreterTests.dir/InterpreterExtensionsTest.cpp.o:InterpreterExtensionsTest.cpp:function (anonymous namespace)::InterpreterExtensionsTest_ExecutorCreateReset_Test::TestBody(): error: undefined reference to 'llvm::detail::TakeError(llvm::Error)'
clang: error: linker command failed with exit code 1 (use -v to see invocation)
```

https://github.com/llvm/llvm-project/pull/84460