beam.Create([...]) does not create an properly shaped PCollection until pipeline executes

This issue is surfaced by the errors from [https://github.com/apache/beam/pull/9077](https://github.com/apache/beam/pull/9077)

Specifically, in the following pipelines, note how Map(lambda x: x) is necessary before the actual transform that is being tested. This is due to the fact that the pcoll output by create is a little odd.
```

// code placeholder
def test_timestamp(self):
l = [TimestampedValue('a', 100),
TimestampedValue('b',
200),
TimestampedValue('c', 300)]
expected = [TestWindowedValue('a', 100, [GlobalWindow()]),

TestWindowedValue('b', 200, [GlobalWindow()]),
TestWindowedValue('c',
300, [GlobalWindow()])]
with TestPipeline() as p:
# Map(lambda x: x) PTransform is added
after Create here, because when
# a PCollection of TimestampedValues is created with Create PTransform,

# the timestamps are not assigned to it. Adding a Map forces the
# PCollection to go through
a DoFn so that the PCollection consists of
# the elements with timestamps assigned to them instead
of a PCollection
# of TimestampedValue(element, timestamp).
pc = p | beam.Create(l) |
beam.Map(lambda x: x)
reified_pc = pc | util.Reify.Timestamp()
assert_that(reified_pc,
equal_to(expected), reify_windows=True)

def test_window(self):
l = [GlobalWindows.windowed_value('a',
100),
GlobalWindows.windowed_value('b', 200),
GlobalWindows.windowed_value('c',
300)]
expected = [TestWindowedValue(('a', 100, GlobalWindow()), 100,

[GlobalWindow()]),
TestWindowedValue(('b', 200, GlobalWindow()), 200,

[GlobalWindow()]),
TestWindowedValue(('c', 300, GlobalWindow()),
300,
[GlobalWindow()])]
with TestPipeline() as p:
pc
= p | beam.Create(l)
# Map(lambda x: x) PTransform is added after Create here, because when

# a PCollection of WindowedValues is created with Create PTransform,
# the windows are not
assigned to it. Adding a Map forces the
# PCollection to go through a DoFn so that the PCollection
consists of
# the elements with timestamps assigned to them instead of a PCollection
#
of WindowedValue(element, timestamp, window).
pc = pc | beam.Map(lambda x: x)
reified_pc
= pc | util.Reify.Window()
assert_that(reified_pc, equal_to(expected), reify_windows=True)

```

Imported from Jira [BEAM-7759](https://issues.apache.org/jira/browse/BEAM-7759). Original Jira may contain additional context.
Reported by: pabloem.