glsl: Rework builtin_variables.cpp to reduce code duplication.

Previously, we had a separate function for setting up the built-in
variables for each combination of shader stage and GLSL version
(e.g. generate_110_vs_variables to generate the built-in variables for
GLSL 1.10 vertex shaders).  The functions called each other in ad-hoc
ways, leading to unexpected inconsistencies (for example,
generate_120_fs_variables was called for GLSL versions 1.20 and above,
but generate_130_fs_variables was called only for GLSL version 1.30).
In addition, it led to a lot of code duplication, since many varyings
had to be duplicated in both the FS and VS code paths.  With the
advent of geometry shaders (and later, tessellation control and
tessellation evaluation shaders), this code duplication was going to
get a lot worse.

So this patch reworks things so that instead of having a separate
function for each shader type and GLSL version, we have a function for
constants, one for uniforms, one for varyings, and one for the special
variables that are specific to each shader type.

In addition, we use a class, builtin_variable_generator, to keep track
of the instruction exec_list, the GLSL parse state, commonly-used
types, and a few other variables, so that we don't have to pass them
around as function arguments.  This makes the code a lot more compact.

Where it was feasible to do so without introducing compilation errors,
I've also gone ahead and introduced the variables needed for
{ARB,EXT}_geometry_shader4 style geometry shaders.  This patch takes
care of everything except the GS variable gl_VerticesIn, the FS
variable gl_PrimitiveID, and GLSL 1.50 style geometry shader inputs
(using the gl_in interface block).  Those remaining features will be
added later.

I've also made a slight nomenclature change: previously we used the
word "deprecated" to refer to variables which are marked in GLSL 1.40
as requiring the ARB_compatibility extension, and are marked in GLSL
1.50 onward as requiring the compatibilty profile.  This was
misleading, since not all deprecated variables require the
compatibility profile (for example gl_FragData and gl_FragColor, which
have been deprecated since GLSL 1.30, but do not require the
compatibility profile until GLSL 4.20).  We now consistently use the
word "compatibility" to refer to these variables.

This patch doesn't introduce any functional changes (since geometry
shaders haven't been enabled yet).

Reviewed-by: Matt Turner <[email protected]>

v2: Rename "typ" -> "type".  Add blank line between inline functions
and declarations in builtin_variable_generator class.  Use the
standard comment "/* FALLTHROUGH */" for compatibility with static
code analysis tools.

Reviewed-by: Kenneth Graunke <[email protected]>

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