This CL allows setting the location of glslangValidator and spirv-remap
when calling the runtests script. A test target is added to CMake to
execute runtests and sets the location to the build folder for the two
applications.

Export glslang targets on installation

find Python and add External subdir only if BUILD_EXTERNAL option was set

find Python and add External subdir only if BUILD_EXTERNAL option was set (on by default) and /External dir exists

Add support for GL_ARB_explicit_uniform_location

Fixed typo in README.md

Remove unnecessary semi-colons and add warning about them

These are causing integration issues with Chromium down stream since
it is more strict about these.

Adjusting code interface

Update spirv-tools known good.

If the semantics that require the KHR form over the EXT form are seen
(OpBitcast between a vector and a pointer) promote the requested extension
from the EXT to the KHR.

The KHR form comes along as part of 1.5, and otherwise should require
another form of request to emit it.

Move install directory for SPIRV/ folder.

Currently the SPIRV/ folder will get installed into the include
directory. This folder is part of GLSLang, so it makes more sense under
glslang/SPIRV.

Currently, GLSLang will install a SPIRV/ folder while spirv-headers will
install a spirv/ folder. This is confusing and will cause issues on a
case sensitive filesystem if both are installed at the same time.

HLSL: Add attributes for image formats and nonreadable/nonwritable

Reflection will crash when the VS input symbol defines the same name with FS output symbol

GLSL/SPV: Fix #1900: Drop const on literal when doing an object copy.

Separate GLSLANG_WEB (min-size build) and Emscripten options

SPV_KHR_physical_storage_buffer/SPV: Add GL_EXT_buffer_reference_uvec2

Adds uvec2 <-> reference constructor support.
Switches from EXT to KHR for physical_storage_buffer.

Fix Fuchsia build.

The Fuchsia build is very picky about newlines at the end of files
and will complain loudly about them. Removing the -Wnewline-eof
warning solves the issue.

Allows building non-min-size builds with Emscripten.
Adds ENABLE_GLSLANG_WEB_DEVEL.
Moves the glslang.js files to OSDependent/Web.
Small cleanups and docs update.

[PURPOSE]:
The current process design for Uniform / Block / Pipe IO symbols reflection (during program linking) is as following :

1.1 using a global mapper called 'TNameToIndex' to store all the relationship of name (of symbols) to their indexes (in their own MapIndexToReflection vectors).

1.2 TNameToIndex mapper will be used during program linking and helps to check and merge duplicate symbols within each stage ( Uniform, Block and Pipe IO)

1.3 Different types of symbols will have their own index mapping storage. All those symbols will share TNameToIndex as a general searching mapper.

1.4 Only IN in first stage and OUT in last stage will be dealed within traversing functions.

Now, here we meet those problems:

2.1 In and Out variables for pipelines are mapping to different MapIndexToReflection vector (ioItems), but they may still have same names within the general symbol search mapper : TNameToIndex.

2.2 Then, when there are same symbols of IN in VS and OUT in FS, TNameToIndex could not tell the difference because it only stores one local index for one symbol (1:1) as a pair of KeyValue.

[What fixed]:

Seperate I/O from other symbols like Uniform and Block (it is wrong to keep them all in TNameToIndex), and save in new searching mappers called pipeInNameToIndex and pipeOutNameToIndex.

Expose new top-level functions defined as getReflectionPipeIOIndex and getPipeIOIndex for users who need to query Pipe I/O information (As they may reach those things through getUniformIndex and getReflectionIndex now, which is a confused way.)

As there are 2 mappers for above symbols, users needs to input second argument when they wanna reach those pipe I/O parameters, that's also why we need to modify GET functions either.

[Test Case]:

The shader is as following:

######### VS ############
layout(location = 0) in vec4 g_position;
layout(location = 1) in vec4 g_color;
out StageData {
vec4 color;
} g_vs_out;
void main() {
gl_Position = g_position;
g_vs_out.color = g_color;
}

########### FS #############
in StageData {
vec4 color;
} g_fs_in;
layout(location = 0) out vec4 g_color;
void main() {
g_color = g_fs_in.color;
}