Fix broken RPath when installing and dynamic linking gtk4-layer-shell

When compiling the dynamic lib and linking, the rpath resolves to the
compile cache location instead of the install location for the lib.
This resulted in loading the dylib failing when the compile cache
was removed or the install location is changed.

Author: AnthonyZhOon

src/build/SharedDeps.zig

@@ -510,7 +510,12 @@ pub fn add(
                     } else {
                         // gtk4-layer-shell *must* be dynamically linked,
                         // so we don't add it as a static library
-                        step.linkLibrary(gtk4_layer_shell.artifact("gtk4-layer-shell"));
+                        const sharedLib = gtk4_layer_shell.artifact("gtk4-layer-shell");
+                        const artifact: *std.Build.Step.InstallArtifact = b.addInstallArtifact(sharedLib, .{});
+                        b.getInstallStep().dependOn(&artifact.step);
+                        // Lookup dynamic libs from installed location
+                        step.root_module.addRPathSpecial("$ORIGIN/../lib/");
+                        step.linkLibrary(sharedLib);
                     }
 
                     step.linkSystemLibrary2("wayland-client", dynamic_link_opts);