arrow

ARROW-4552: [JS] Add high-level Table and Column convenience methods

This PR closes the following JIRAs:

* [ARROW-4552](https://issues.apache.org/jira/browse/ARROW-4552) - Add Table and Schema `assign(other)` implementations
* [ARROW-2764](https://issues.apache.org/jira/browse/ARROW-2764) - Easy way to create a new Table with an additional column
* [ARROW-4553](https://issues.apache.org/jira/browse/ARROW-4553) - Implement Schema/Field/DataType comparators
* [ARROW-4554](https://issues.apache.org/jira/browse/ARROW-4554) - Implement logic for combining Vectors with different lengths/chunksizes
* [ARROW-4555](https://issues.apache.org/jira/browse/ARROW-4555) - Add high-level Table and Column creation methods
* [ARROW-4557](https://issues.apache.org/jira/browse/ARROW-4557) - Add Table/Schema/RecordBatch `selectAt(...indices)` method

I extracted a few more  high-level helper methods I've had laying around for creating, selecting, or manipulating Tables/Columns/Schemas/RecordBatches.

1. We currently have a `table.select(...colNames)` implementation, so I also added a `table.selectAt(...colIndices)` method to complement. Super handy when you have duplicates.
2. I added a basic `table.assign(otherTable)` impl. I added logic to compare Schemas/Fields/DataTypes in order to de-dupe reliably, which lives in the [`TypeComparator` Visitor](https://github.com/trxcllnt/arrow/blob/a67bd562cf6c4860bdce027981df859398e41b6d/js/src/visitor/typecomparator.ts#L83). I expose this via `compareTo()` methods on the Schema, Field, and DataType for ease of use. Bonus: the Writer [can now discern](https://github.com/trxcllnt/arrow/blob/a67bd562cf6c4860bdce027981df859398e41b6d/js/src/ipc/writer.ts#L129) between RecordBatches of the same stream whose Schemas aren't reference-equal.
3. I've also added logic to distribute Vectors of different lengths (or different internal chunk sizes) evenly across RecordBatches, to support a nearly zero-copy `Table#assign()` impl. I say nearly zero-copy, because there's a bit of allocation/copying to backfill null bitmaps if chunks don't exactly line up. But this also means [it's a bit easier](https://github.com/trxcllnt/arrow/blob/a67bd562cf6c4860bdce027981df859398e41b6d/js/test/unit/table-tests.ts#L178) now to create Tables or RecordBatches from values in-memory whose lengths may not exactly line up:
```ts
const table = Table.new(
  Column.new('foo', IntVector.from(arange(new Int32Array(10))),
  Column.new('bar', FloatVector.from(arange(new Float32Array(100))))
);
```
4. And lastly, I added [some more more tests](https://github.com/trxcllnt/arrow/blob/js/high-level-table-column-fns/js/test/unit/table/serialize-tests.ts#L38) to ensure various combinations of select/slice/concat/assign can round-trip through IPC and back again.

```ts

const table1 = Table.new(
    Column.new('a', Int32Vector.from(i32s)),
    Column.new('b', Float32Vector.from(f32s)),
    Column.new('c', Float64Vector.from(f64s))
);

const table2 = Table.new(
    Column.new('d', Utf8Vector.from(strs)),
    Column.new('d', BoolVector.from(bools)),
    Column.new('d', Int32Vector.from(i32s)),
);

const table3 = table1.select('b', 'c').assign(table2.selectAt(0, 1));

console.log(table3.schema.fields)
// > [
// >     ('b', Float32),
// >     ('c', Float64),
// >     ('d', Utf8),
// >     ('d', Bool)
// > ]
```
(cc: @domoritz)

Author: ptaylor <paul.e.taylor@me.com>

Closes #3634 from trxcllnt/js/high-level-table-column-fns and squashes the following commits:

9943d9c2 <ptaylor> fix lint
4b8fb547 <ptaylor> add a test for table and recordbatch with a single column
17580639 <ptaylor> add Table.new docstring
bfbcc8b6 <ptaylor> cleanup/rename Table + Schema + RecordBatch from -> new, cleanup argument extraction util fns
5b6d938d <ptaylor> cleanup
98c8e525 <ptaylor> add initial RecordBatch.new and select tests
dc801434 <ptaylor> remove Table.fromVectors in favor of Table.new
73b8af7d <ptaylor> fix Int64Vector typings
83de5ed0 <ptaylor> guard against out-of-bounds selections
a67bd562 <ptaylor> clean up: eliminate more getters in favor of read-only properties
7a8daada <ptaylor> clean up/speed up: move common argument flattening methods into a utility file
41aa9024 <ptaylor> Add more tests to ensure Tables can serialize through various slice, concat, assign steps
07a2c964 <ptaylor> add basic Table#assign tests
e4a5d870 <ptaylor> split out the generated data validators for reuse
99e88883 <ptaylor> add Table and Schema assign() impls
0ac786c7 <ptaylor> add selectAt() method to Table, Schema, and RecordBatch for selecting columns by index
cf6f97ac <ptaylor> add TypeComparator visitor so we can compare Schemas, Fields, and DataTypes
b2153aa1 <ptaylor> ensure the Vector map types always fall back to BaseVector
9d8f4938 <ptaylor> cleanup: use the specialized typed array casting functions
85d0e001 <ptaylor> fix uniform chunk distribution when the new chunks are longer than the current chunks
8218f404 <ptaylor> Ensure Chunked#slice() range end is correct when there's only a single chunk
3f16c813 <ptaylor> fix typo
c9eeb056 <ptaylor> fix lint
933b5312 <ptaylor> Narrow the signature of Schema#fields to Field<T>, cleanup
bdb23b83 <ptaylor> ensure uniform chunk lengths in RecordBatch.from()
9d1f2ade <ptaylor> add Table.new() convenience method for creating Tables from Columns or , name | Field] arguments
0407cd74 <ptaylor> add Column.new() convenience method for creating Columns with string names and polymorphic chunk types
db390311 <ptaylor> add public Field#clone impl for convenience
97c349e8 <ptaylor> add nullable and metadata getters to the Column class
5dfc1007 <ptaylor> make the abstract Vector a type alias to trick TS into letting us override static methods
6ddfaf83 <ptaylor> narrow the FloatVector.from() return signatures