HLSL: add missing vec,vec,scalar form of lerp(), + test

Test/hlsl.intrinsics.frag

@@ -223,6 +223,7 @@ float3 PixelShaderFunction3(float3 inF0, float3 inF1, float3 inF2, uint3 inU0, u
     bool3 r041 = isnan(inF0);
     float3 r042 = ldexp(inF0, inF1);
     float3 r039a = lerp(inF0, inF1, inF2);
+    float3 r039b = lerp(inF0, inF1, 0.3); // test vec,vec,scalar lerp
     float r043 = length(inF0);
     float3 r044 = log(inF0);
     float3 r045 = log10(inF0);

hlsl/hlslParseables.cpp

@@ -531,7 +531,8 @@ void TBuiltInParseablesHlsl::initialize(int /*version*/, EProfile /*profile*/, c
         { "isnan",                            nullptr, "B" ,      "SVM",            "F",             EShLangAll },
         { "ldexp",                            nullptr, nullptr,   "SVM,",           "F,",            EShLangAll },
         { "length",                           "S",     "F",       "V",              "F",             EShLangAll },
-        { "lerp",                             nullptr, nullptr,   "SVM,,",          "F,,",           EShLangAll },
+        { "lerp",                             nullptr, nullptr,   "VM,,",           "F,,",           EShLangAll },
+        { "lerp",                             nullptr, nullptr,   "SVM,,S",         "F,,",           EShLangAll },
         { "lit",                              "V4",    "F",       "S,,",            "F,,",           EShLangAll },
         { "log",                              nullptr, nullptr,   "SVM",            "F",             EShLangAll },
         { "log10",                            nullptr, nullptr,   "SVM",            "F",             EShLangAll },