Migrate from VecCore and Vc to std::experimental::simd

Use `std::experimental::simd` for the vectorized TMath and vectorized
TFormula backend if available. We assume it's available if ROOT is
compiled with C++20 or later on Linux. In reality, it is avialble for
new-enough Clang and GCC compilers (GCC >= 11), but it is not worth it
at this point to check the compiler version explicitly, to keep things
simple. People who build with C++20 are also expected to use new
compilers.

The fact that ROOT C++17 users lose the vectorized TMath and TFormula
features is an acceptable collateral damage of this migration, as the
features are rarely used and the code/build system simplification is
significant. If users really relied on these niche features, they are
expected to build with C++20.

Windows and Apple silicon users are unaffected by this migration. The
VecCore+Vc combination did not compile on Windows before anyway, and Vc
does not support Apple silicon as Vc didn't support vectorization on ARM
via Neon (it was [in developement](https://github.com/VcDevel/Vc?tab=readme-ov-file#vc-portable-zero-overhead-c-types-for-explicitly-data-parallel-programming) but never finished).

As a result of this migration, the `vc`, `veccore`, `builtin_vc`, and
`builtin_veccore` build options are deprecated.

The migration also fixes this long-standing JIRA issue about failing
TFormula vectorization tests, because Vc symbols could not be resolved:
https://its.cern.ch/jira/browse/ROOT-10614
This was a fundamental limitation of the statically-linked Vc library,
as symbols could not be looked up by the interpreter at runtime. This
limitation is gone with the migration to `std::experimental::simd`.

The unit test that checks if GenVector works with Vc types was changed
to use `std::experimental::simd` types instead.

Author: guitargeek

lib/Interpreter/CMakeLists.txt

@@ -58,10 +58,6 @@ set(LLVM_LINK_COMPONENTS
   ${LLVM_TARGETS_TO_BUILD}
 )
 
-if (vc)
-  set(cling_vc_support ON)
-endif()
-
 # clingInterpreter depends on Options.inc to be tablegen-ed
 # (target ClangDriverOptions) from in-tree builds.
 set(CLING_DEPENDS ClingDriverOptions)
@@ -375,10 +371,6 @@ add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/cling-compiledata.h
 set_property(SOURCE ${CMAKE_CURRENT_SOURCE_DIR}/CIFactory.cpp
              APPEND PROPERTY OBJECT_DEPENDS
              ${CMAKE_CURRENT_BINARY_DIR}/cling-compiledata.h)
-if(cling_vc_support)
-  set_property(SOURCE ${CMAKE_CURRENT_SOURCE_DIR}/CIFactory.cpp
-               APPEND PROPERTY COMPILE_DEFINITIONS "CLING_SUPPORT_VC")
-endif()
 
 # If LLVM is external, but Clang is builtin, we must use some files
 # from patched (builtin) version of LLVM