ggml-openvino : fix clangd and MSVC warnings, enforce internal linkage

[mostafafaheem]

It's a huge diff but it's mostly copy pasting functions around to fix undeclared errors

1. Enforces internal linkage when possible, in ggml-quants.h / ggml-quants.cpp, utils.h / utils.cpp, openvino/utils.h / openvino/utils.cpp. Not exhaustive, since some utilities might need to be public, so limited to functions only used once, like graph compute, weight extraction, quantize_*, etc.
2. Fixes clangd linter warnings about using std::endl, unused includes and pragmas, using const and const reference when possible, calling static GgmlOvDecoder methods by their class instead of an instance, integer to pointer casting, and other minimal changes.
3. Fixes 1 MSVC warning about mismatched types.

No functional differences otherwise.