Hide exposed utility functions in collections

[austinabell]

Some utility functions, which should not be exposed publicly, should just be converted into internal functions to avoid confusion and make this change less breaking in the future.

Offending functions:

near-sdk-js/src/collections/unordered-map.js

Lines 35 to 51 in 37965b8

	serializeIndex(index) {
	let data = new Uint32Array([index])
	let array = new Uint8Array(data.buffer)
	return u8ArrayToBytes(array)
	}
	deserializeIndex(rawIndex) {
	let array = bytesToU8Array(rawIndex)
	let data = new Uint32Array(array.buffer)
	return data[0]
	}
	getIndexRaw(key) {
	let indexLookup = this.keyIndexPrefix + key
	let indexRaw = near.jsvmStorageRead(indexLookup)
	return indexRaw
	}

near-sdk-js/src/collections/unordered-set.js

Lines 23 to 33 in 37965b8

	serializeIndex(index) {
	let data = new Uint32Array([index])
	let array = new Uint8Array(data.buffer)
	return u8ArrayToBytes(array)
	}
	deserializeIndex(rawIndex) {
	let array = bytesToU8Array(rawIndex)
	let data = new Uint32Array(array.buffer)
	return data[0]
	}

https://github.com/near/near-sdk-js/blob/master/src/collections/vector.js#L23-L28

[ailisp]

Duplicated with #83

[austinabell]

Duplicated with #83

oops, I really do have a bad memory 😂