build-system: Replace deprecated usages of addStaticLibrary with addLibrary (#8029)

Hi there, this is just a low-hanging fruit and it also prepares the way
for the future 0.15, which removes addStaticLibrary.
Please, let me know what to do on the `// TODO` comments.

pkg/utfcpp/build.zig

@@ -4,10 +4,13 @@ pub fn build(b: *std.Build) !void {
     const target = b.standardTargetOptions(.{});
     const optimize = b.standardOptimizeOption(.{});
 
-    const lib = b.addStaticLibrary(.{
+    const lib = b.addLibrary(.{
         .name = "utfcpp",
-        .target = target,
-        .optimize = optimize,
+        .root_module = b.createModule(.{
+            .target = target,
+            .optimize = optimize,
+        }),
+        .linkage = .static,
     });
     lib.linkLibCpp();