Move hlsl/ source to glslang/HLSL/

Now that the HLSL source files are part of the `glslang` target (#2271), it makes sense for these to sit in the `glslang` directory.

Changed the case of the directory from `hlsl` to `HLSL` to better match the sibling directories.

hlsl/pch.cpp

@@ -1,35 +0,0 @@
-//
-// Copyright (C) 2018 The Khronos Group Inc.
-// All rights reserved.
-//
-// Redistribution and use in source and binary forms, with or without
-// modification, are permitted provided that the following conditions
-// are met:
-//
-//    Redistributions of source code must retain the above copyright
-//    notice, this list of conditions and the following disclaimer.
-//
-//    Redistributions in binary form must reproduce the above
-//    copyright notice, this list of conditions and the following
-//    disclaimer in the documentation and/or other materials provided
-//    with the distribution.
-//
-//    Neither the name of 3Dlabs Inc. Ltd. nor the names of its
-//    contributors may be used to endorse or promote products derived
-//    from this software without specific prior written permission.
-//
-// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
-// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
-// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
-// FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
-// COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
-// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
-// BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
-// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
-// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
-// LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
-// ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
-// POSSIBILITY OF SUCH DAMAGE.
-//
-
-#include "pch.h"