[PE] fix read context EDT juggling in FlutterInitializer

[pq]

The move to project activities has some nuance. In the long run we'll be able to do some real performance tuning but in the short-run some of our assumptions about being in a read context need to be rethunk. Here's one.

The rub is autoCreateRunConfig needs to be in a read context but the remaining initialization needs to be on the EDT.

Fixes #8215

See also: #8100

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