…s newline delimited json streams

## Rationale
Currently the Arrow json writer makes JSON that looks like this (one record per line):
```json
{"foo":1}
{"bar":1}
```

Which is not technically valid JSON, which would look something like this:

```
[
  {"foo":1},
  {"bar":1}
]
```

## New Features
This PR parameterizes the JSON writer so it can write in either format. Note I needed this feature for in IOx, in influxdata/influxdb_iox#870, and I want to propose contributing it back here).

## Other Changes:
1. Added the function `into_inner()` to retrieve the inner writer from the JSON writer, following the model of the Rust standard library (e.g. [BufReader::into_inner](https://doc.rust-lang.org/std/io/struct.BufReader.html#method.into_inner)

2. Per Rust standard pattern, I change the JSON writer so that it doesn't add any Buffering (via `BufReader`) itself, and instead allows the caller the choice of what type of buffering, if any, is needed.

3. Added / cleaned up a bunch of documentation and comments.

## Questions
I went with parameterizing the `Writer` output as a trait rather than runtime dispatch, for performance. This shouldn't have backwards compatible issues Given the writer has not yet been released yet (introduced by @houqp #9256)

However would people prefer a single `Writer` that took an `Options` struct or something to determine how it wrote out data?

Closes #9575 from alamb/alamb/json_arrays

Authored-by: Andrew Lamb <[email protected]>
Signed-off-by: Andrew Lamb <[email protected]>

…s newline delimited json streams

## Rationale
Currently the Arrow json writer makes JSON that looks like this (one record per line):
```json
{"foo":1}
{"bar":1}
```

Which is not technically valid JSON, which would look something like this:

```
[
  {"foo":1},
  {"bar":1}
]
```

## New Features
This PR parameterizes the JSON writer so it can write in either format. Note I needed this feature for in IOx, in influxdata/influxdb_iox#870, and I want to propose contributing it back here).

## Other Changes:
1. Added the function `into_inner()` to retrieve the inner writer from the JSON writer, following the model of the Rust standard library (e.g. [BufReader::into_inner](https://doc.rust-lang.org/std/io/struct.BufReader.html#method.into_inner)

2. Per Rust standard pattern, I change the JSON writer so that it doesn't add any Buffering (via `BufReader`) itself, and instead allows the caller the choice of what type of buffering, if any, is needed.

3. Added / cleaned up a bunch of documentation and comments.

## Questions
I went with parameterizing the `Writer` output as a trait rather than runtime dispatch, for performance. This shouldn't have backwards compatible issues Given the writer has not yet been released yet (introduced by @houqp apache/arrow#9256)

However would people prefer a single `Writer` that took an `Options` struct or something to determine how it wrote out data?

Closes #9575 from alamb/alamb/json_arrays

Authored-by: Andrew Lamb <[email protected]>
Signed-off-by: Andrew Lamb <[email protected]>