feat: Add custom formatters for Shader::IR::Inst in formatters.h

- Created a new header file `formatters.h` under `shader_recompiler/frontend/ir/`.
- Added a custom `fmt::formatter` specialization for the `Shader::IR::Inst` type.
- This allows `Shader::IR::Inst` objects to be formatted using `fmt::format`, `fmt::print`, and similar functions from the `fmt` library.
- The formatter uses the `ToString` method of `Shader::IR::Inst` to generate a formatted string representation.

src/shader_recompiler/frontend/ir/formatters.h

@@ -0,0 +1,20 @@
+// shader_recompiler/frontend/ir/formatters.h
+
+#pragma once
+#include <fmt/format.h>
+#include "shader_recompiler/frontend/ir/value.h"
+
+namespace Shader::IR {
+    // Custom formatter for Shader::IR::Inst
+    template <>
+    struct fmt::formatter<Shader::IR::Inst> {
+        constexpr auto parse(fmt::format_parse_context& ctx) {
+            return ctx.begin();
+        }
+
+        template <typename FormatContext>
+        auto format(const Shader::IR::Inst& inst, FormatContext& ctx) {
+            return fmt::format_to(ctx.out(), "{}", inst.ToString());
+        }
+    };
+}