4913c92c2f
## What changes were proposed in this pull request?
Right now file source always uses `InMemoryFileIndex` to scan files from a given path.
But when reading the outputs from another streaming query, the file source should use `MetadataFileIndex` to list files from the sink log. This patch adds this support.
## `MetadataFileIndex` or `InMemoryFileIndex`
```scala
spark
.readStream
.format(...)
.load("/some/path") // for a non-glob path:
// - use `MetadataFileIndex` when `/some/path/_spark_meta` exists
// - fall back to `InMemoryFileIndex` otherwise
```
```scala
spark
.readStream
.format(...)
.load("/some/path/*/*") // for a glob path: always use `InMemoryFileIndex`
```
## How was this patch tested?
two newly added tests
Author: Liwei Lin <lwlin7@gmail.com>
Closes #16987 from lw-lin/source-read-from-sink.
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