break dependency of Program on SamplerInterfaceBlock and SamplerBindingMap

Instead of passing SamplerInterfaceBlocks and a SamplerBindingMap to
Program, we now set a 'sampler group' per binding point:

Program::addSamplerGroup(...)

A sampler group here consists of a list of N 'Sampler' and a 'Sampler'
is just a unique name (unifrom name in the shader) and binding point in
the shader.

That's all the driver layer needs.

With this change we get rid of the code that re-created the uniform
names in the driver -- this should never have been done there. And we
also remove the hash-map lookups in vulkan and metal drivers.

libs/utils/src/CString.cpp

@@ -33,11 +33,11 @@ int StaticString::compare(const StaticString& rhs) const noexcept {
 // ------------------------------------------------------------------------------------------------
 
 UTILS_NOINLINE
-CString::CString(const char* cstr, size_type length) {
+CString::CString(const char* cstr, size_t length) {
     if (length && cstr) {
         assert(length == strlen(cstr));
         Data* p = (Data*)malloc(sizeof(Data) + length + 1);
-        p->length = length;
+        p->length = (size_type)length;
         mCStr = (value_type*)(p + 1);
         // we don't use memcpy here to avoid a call to libc, the generated code is pretty good.
         std::uninitialized_copy_n(cstr, length + 1, mCStr);