[SYCL][Doc] Move invoke_simd extension doc to 'experimental' as implementation is available. (#6585)

Signed-off-by: Konstantin S Bobrovsky <[email protected]>

Author: kbobrovs

sycl/doc/extensions/proposed/sycl_ext_oneapi_invoke_simd.asciidoc renamed to sycl/doc/extensions/experimental/sycl_ext_oneapi_invoke_simd.asciidoc

@@ -17,7 +17,6 @@
 :language: {basebackend@docbook:c++:cpp}
 
 == Introduction
-IMPORTANT: This specification is a draft.
 
 NOTE: Khronos(R) is a registered trademark and SYCL(TM) and SPIR(TM) are trademarks of The Khronos Group Inc.  OpenCL(TM) is a trademark of Apple Inc. used by permission by Khronos.
 
@@ -30,13 +29,13 @@ Copyright (c) 2021-2022 Intel Corporation.  All rights reserved.
 
 == Status
 
-Working Draft
+Experimental
 
-This is a proposed extension specification, intended to gather community
-feedback. Interfaces defined in this specification may not be implemented yet
-or may be in a preliminary state. The specification itself may also change in
-incompatible ways before it is finalized. Shipping software products should not
-rely on APIs defined in this specification.
+This is an experimental extension specification, intended to provide early
+access to features and gather community feedback. Interfaces defined in this
+specification are implemented in DPC++, but they are not finalized and may
+change incompatibly in future versions of DPC++ without prior notice. Shipping
+software products should not rely on APIs defined in this specification.
 
 == Version