fix: measure and profile builds,shorebird patch ios takes longer that necessary

[eseidel]

As part of adding our linker to dart compiles, we now compile the code 3 times when making a patch. This probably isn't the slow part of an iOS build (xcode itself tends to take a very long time), but it does contribute.

We should be able to reduce this to only one compile pass with a bit more modification to the Dart toolchain.

The real fix here is to measure and profile our build times.