## What changes were proposed in this pull request?
Currently in `StreamTest`, we have a `StartStream` which will start a streaming query against trigger `ProcessTime(intervalMS = 0)` and `SystemClock`.
We also need to test cases against `ProcessTime(intervalMS > 0)`, which often requires `ManualClock`.
This patch:
- fixes an issue of `ProcessingTimeExecutor`, where for a batch it should run `batchRunner` only once but might run multiple times under certain conditions;
- adds support for testing against the `ProcessingTime(intervalMS > 0)` trigger and `AdvanceManualClock`, by specifying them as fields for `StartStream`, and by adding an `AdvanceClock` action;
- adds a test, which takes advantage of the new `StartStream` and `AdvanceManualClock`, to test against [PR#[SPARK-14942] Reduce delay between batch construction and execution ](https://github.com/apache/spark/pull/12725).
## How was this patch tested?
N/A
Author: Liwei Lin <lwlin7@gmail.com>
Closes#12797 from lw-lin/add-trigger-test-support.
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