[react] store transform callback in useRef

[mrmonat]

This should fix #1131

I think because the old implementation did not persist the callback between renders, the transform method of the form helper had no effect (was reset to default (data) => data callback) when called like shown in the example in issue #1131

[mxmtsk]

I ran into the same issue and can confirm that this fixes the issue.

[ashlimx]

Can we please put priority on this pull request? It's not great the documented transform feature just 100% does not work at all for this long with an active fix available

[mahangm]

Is there no update on this PR?

[Jamesking56]

This looks like it needs rebasing as it has a bunch of other unrelated changes in it

[ghost]

This is a huge update! Can confirm this is working as expected. How can we get this merged? These are the only changes which are needed:

https://github.com/inertiajs/inertia/pull/1171/commits/53b40db1beaef3b366ad738de1c956572e1b1c69

[mrmonat]

#1491 is newer.