[SYCL][DOC] Change extension names to lower case (#5607)

I found the all-upper-case names difficult to read, especially in a
directory listing where all the files are upper case.  Change them all
to lower case.  The name of the extension and the name of the file are
now lower case.  The name of the feature-test macro remains upper case.

Author: gmlueck

sycl/ReleaseNotes.md

@@ -58,7 +58,7 @@ __SYCL_INLINE_CONSTEXPR bool is_group_v =
 namespace detail {
 // Type for Intel device UUID extension.
 // For details about this extension, see
-// sycl/doc/extensions/supported/SYCL_EXT_INTEL_DEVICE_INFO.md
+// sycl/doc/extensions/supported/sycl_ext_intel_device_info.md
 using uuid_type = std::array<unsigned char, 16>;
 
 template <typename T, typename R> struct copy_cv_qualifiers;

sycl/doc/EnvironmentVariables.md

@@ -15,7 +15,7 @@
 /// @defgroup sycl_esimd DPC++ Explicit SIMD API
 /// This is a low-level API providing direct access to Intel GPU hardware
 /// features. ESIMD overview can be found
-/// [here](https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/experimental/SYCL_EXT_INTEL_ESIMD/SYCL_EXT_INTEL_ESIMD.md).
+/// [here](https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/experimental/sycl_ext_intel_esimd/sycl_ext_intel_esimd.md).
 /// Some terminology used in the API documentation:
 /// - *lane* -
 ///       (or "vector lane") Individual "lane" of input and output elements

sycl/doc/GetStartedGuide.md

@@ -35,7 +35,7 @@ std::enable_if_t<std::is_trivially_destructible<T>::value &&
   return reinterpret_cast<__attribute__((opencl_local)) T *>(AllocatedMem);
 #else
   throw feature_not_supported(
-      "SYCL_EXT_ONEAPI_LOCAL_MEMORY extension is not supported on host device",
+      "sycl_ext_oneapi_local_memory extension is not supported on host device",
       PI_INVALID_OPERATION);
 #endif
 }
@@ -60,7 +60,7 @@ std::enable_if_t<std::is_trivially_destructible<T>::value &&
   // Silence unused variable warning
   [&args...] {}();
   throw feature_not_supported(
-      "SYCL_EXT_ONEAPI_LOCAL_MEMORY extension is not supported on host device",
+      "sycl_ext_oneapi_local_memory extension is not supported on host device",
       PI_INVALID_OPERATION);
 #endif
 }

sycl/doc/MultiTileCardWithLevelZero.md

@@ -1744,7 +1744,7 @@ pi_result cuda_piDeviceGetInfo(pi_device device, pi_device_info param_name,
   case PI_DEVICE_INFO_MAX_MEM_BANDWIDTH:
     // TODO: Check if Intel device UUID extension is utilized for CUDA.
     // For details about this extension, see
-    // sycl/doc/extensions/supported/SYCL_EXT_INTEL_DEVICE_INFO.md
+    // sycl/doc/extensions/supported/sycl_ext_intel_device_info.md
   case PI_DEVICE_INFO_UUID:
     return PI_INVALID_VALUE;