[SYCL][Docs] Move sycl_ext_intel_event_mode to experimental (#18417)

This commit moves the sycl_ext_intel_event_mode extension to the
experimental namespace and defines the corresponding feature test macro.

---------

Signed-off-by: Larsen, Steffen <[email protected]>

Author: steffenlarsen

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

@@ -52,11 +52,12 @@ This extension also depends on the following other SYCL extensions:
 
 == Status
 
-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 {dpcpp}, but they are not finalized and may
+change incompatibly in future versions of {dpcpp} without prior notice.
+*Shipping software products should not rely on APIs defined in this
+specification.*
 
 
 == Overview

sycl/source/feature_test.hpp.in

@@ -120,6 +120,7 @@ inline namespace _V1 {
 // In progress yet
 #define SYCL_EXT_ONEAPI_ATOMIC16 0
 #define SYCL_KHR_DEFAULT_CONTEXT 1
+#define SYCL_EXT_INTEL_EVENT_MODE 1
 
 #ifndef __has_include
 #define __has_include(x) 0