Store pending override config instead of creating ActivityClientRecord

Create ActivityClientRecord early in preExecute may cause
NullPointerException. If two LaunchActivityItem using the same token
and the 1st postExecute() comes after 2nd preExecute(), the
corresponding launching activity will be removed and cause 2nd
execute() get NullPointerException.

Since the only use case to get ActivityClientRecord in preExecute() is
just to use it to store the pending override config. We can directly
store the latest pending override config from preExecute() in
ActivityThread instead of creating ActivityClientRecord.

Bug: 201668069
Test: atest TransactionExecutorTests
      atest ActivityThreadTest
Merged-In: If350e942254e54c9ec90bc63a6e50eb67d038183
Change-Id: If350e942254e54c9ec90bc63a6e50eb67d038183