lavfi: add Vulkan filtering framework

This commit adds a Vulkan filtering infrastructure for libavfilter.
It attempts to abstract as much as possible of the Vulkan API from filters.

The way the hwcontext and the framework are designed permits for parallel,
non-CPU-blocking filtering throughout, with the exception of up/downloading
and mapping.

configure

@@ -236,6 +236,7 @@ External library support:
   --enable-libfontconfig   enable libfontconfig, useful for drawtext filter [no]
   --enable-libfreetype     enable libfreetype, needed for drawtext filter [no]
   --enable-libfribidi      enable libfribidi, improves drawtext filter [no]
+  --enable-libglslang      enable GLSL->SPIRV compilation via libglslang [no]
   --enable-libgme          enable Game Music Emu via libgme [no]
   --enable-libgsm          enable GSM de/encoding via libgsm [no]
   --enable-libiec61883     enable iec61883 via libiec61883 [no]
@@ -1550,11 +1551,11 @@ require_cc(){
 }
 
 require_cpp(){
-    name="$1"
-    headers="$2"
-    classes="$3"
-    shift 3
-    check_lib_cpp "$headers" "$classes" "$@" || die "ERROR: $name not found"
+    log require_cpp "$@"
+    name_version="$1"
+    name="${1%% *}"
+    shift
+    check_lib_cpp "$name" "$@" || die "ERROR: $name_version not found"
 }
 
 require_headers(){
@@ -1771,6 +1772,7 @@ EXTERNAL_LIBRARY_LIST="
     libfontconfig
     libfreetype
     libfribidi
+    libglslang
     libgme
     libgsm
     libiec61883
@@ -6261,6 +6263,7 @@ enabled fontconfig        && enable libfontconfig
 enabled libfontconfig     && require_pkg_config libfontconfig fontconfig "fontconfig/fontconfig.h" FcInit
 enabled libfreetype       && require_pkg_config libfreetype freetype2 "ft2build.h FT_FREETYPE_H" FT_Init_FreeType
 enabled libfribidi        && require_pkg_config libfribidi fribidi fribidi.h fribidi_version_info
+enabled libglslang        && require_cpp libglslang glslang/SPIRV/GlslangToSpv.h "glslang::TIntermediate*" -lglslang -lOSDependent -lHLSL -lOGLCompiler -lSPVRemapper -lSPIRV -lSPIRV-Tools -lSPIRV-Tools-opt -lpthread -lstdc++
 enabled libgme            && { check_pkg_config libgme libgme gme/gme.h gme_new_emu ||
                                require libgme gme/gme.h gme_new_emu -lgme -lstdc++; }
 enabled libgsm            && { for gsm_hdr in "gsm.h" "gsm/gsm.h"; do