Update the default value of fill_dialog_timeout_ms from 300ms to 400ms.

Test: atest CtsAutoFillServiceTestCases
Flag: android.service.autofill.improve_fill_dialog_aconfig
Bug: 406323161
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:a0fa8470cffde222b1d9981e6f95f4f4f167bb50)
Merged-In: Ia8f858e607a1e07a77efa6f71215a81bf4c997ed
Change-Id: Ia8f858e607a1e07a77efa6f71215a81bf4c997ed