Merge pull request #20546 from sivanov-work:initial_vpl_source

G-API: oneVPL (simplification) source base commit

* oneVPL source initial

* Fix compilation

* Fix compilation path

* Fix NO VPL compile

* Fix unused vars

* Fix unused vars in example

* Simplify oneVPL search: no custom path & download

* Fix standalone GAPI

* Apply comments

modules/gapi/cmake/init.cmake

@@ -32,3 +32,10 @@ if(WITH_PLAIDML)
       set(HAVE_PLAIDML TRUE)
   endif()
 endif()
+
+if(WITH_GAPI_ONEVPL)
+    find_package(VPL)
+    if(VPL_FOUND)
+        set(HAVE_GAPI_ONEVPL TRUE)
+    endif()
+endif()