[clang] [HLSL] Move `_init_resource_bindings` to entry point functions (PR #119311)

[Helena Kotas via cfe-commits]

hekota wrote:

> Is this the right solution, or should we be doing something to force the constructor function to be generated? I'm a little worried that we have one path for initializing some types of globals and a different approach for other globals.

I'll see if I can move creation of the `cbuffer` global variable right after it is declared and that should get captured by the module init. We might still need to generate the body of the resource init function later in codegen.

https://github.com/llvm/llvm-project/pull/119311