Enable decimal128 test

[kylebarron]

I'm not sure why this is failing, but it seems like it might point to an Arrow JS bug. In particular, the decimal array written by pyarrow is

arrow-js-ffi/tests/pyarrow_generate_data.py

Line 61 in f9ae0be

[Decimal("1.23"), Decimal("2.67"), Decimal("4.93")], type=pa.decimal128(10, 3)

I'm not sure how to interpret the console.log output from here

arrow-js-ffi/tests/ffi.test.ts

Lines 390 to 391 in f9ae0be

	console.log(originalVector.get(0));
	console.log(wasmVector.get(0));

DecimalBigNum(4) [Uint32Array] [ 1230, 0, 0, 0 ]
DecimalBigNum(3) [Uint32Array] [ 1230, 0, 0 ]

[kylebarron]

Looks like the same error as apache/arrow-js#77