Add support to convert strings to large integer and address ScVals

[Shaptic]

In summary, this adds the following conversions:

• JS string -> ScVal with an ScAddress
• JS string -> ScVal with large integers such as Int128Parts (accomplished via XdrLargeInt)

For details, you can refer to the changes in test/unit/scval_test.js for new usage examples.

Closes #683.

---

An unrelated change is to tests.yml which actually does prettier formatting before checking the diff 🤦. This is the cause of a handful of formatting changes (yarn fmt wasn't run in a previous PR).

[github-actions]

Size Change: +7.17 kB (0%)

Total Size: 3.13 MB

Filename	Size	Change
dist/stellar-base.js	2.3 MB	+5.3 kB (0%)
dist/stellar-base.min.js	835 kB	+1.87 kB (0%)

_{compressed-size-action}

[sreuland]

I know this is unchanged, but would it make sense to call isType(scvType) here and jsdoc that it throws if scvType invalid?

[Shaptic]

I thought this was a good idea so I gave it a shot, but then I realized two things:

• this shouldn't ever be called by clients, honestly, so I made it private in 7de0557 (it was only exported for tests)
• the non-int cases are already covered by scValToBigInt, here: https://github.com/stellar/js-stellar-base/blob/scval-better-ints/src/numbers/index.js#L57

So this check would just add unnecessary internal overhead. If we ever need to make this public, we should definitely do the check!

[sreuland]

is it worth adding a line or separate test case, to demonstrate expectation when invalid

XdrLargeInt.getType('ab');

[Shaptic]

good call! but this is implicitly already handled by an existing test case, here:

js-stellar-base/test/unit/scint_test.js

Lines 247 to 251 in 25a2b68

	it('throws for non-integers', function () {
	expect(() =>
	StellarBase.scValToBigInt(new xdr.ScVal.scvString('hello'))
	).to.throw(/integer/i);
	});