feat(NODE-5594): add Decimal128.fromStringWithRounding() static method

[W-A-James]

Description

What is changing?

• Adds Decimal128.fromStringWithRounding static method
• Convert test/node/decimal128_tests.js to typescript and add tests for fromStringWithRounding

Is there new documentation needed for these changes?

• Yes, DOCSP ticket will be filed

What is the motivation for this change?

NODE-5594

Release Highlight

Adds new Decimal128.fromStringWithRounding static method

Prior to the 6.0.0 release, Decimal128.fromString performed rounding behaviour by default that rounded numbers with >34 significant digits incorrectly. In addition to this bug, the intention of the Decimal128 type and specification is to provide an interface to a high-precision floating point value, so rounding by default also went against this intention, which is why that behaviour was removed from the method in the 6.0.0 release.

We understand that some users may have come to rely on the rounding behaviour, so that has been corrected here and exposed via a new static method, Decimal128.fromStringWithRounding, which should now allow these users to migrate to the v6 of the driver.

Thank you to @hconn-riparian for reporting a related rounding bug and fix in #560 which has been included in this feature.

// 5.x
> let d = Decimal128.fromString('127341286781293491234791234667890123')
new Decimal128("1.273412867812934912347912346678901E+35")

// 6.x
> let d = Decimal128.fromString('127341286781293491234791234667890123')
Uncaught:
BSONError: "127341286781293491234791234667890123" is not a valid Decimal128 string - inexact rounding
    at invalidErr (./js-bson/lib/bson.cjs:1402:11)
    at Decimal128.fromStringInternal (./js-bson/lib/bson.cjs:1633:25)
    at Decimal128.fromString (./js-bson/lib/bson.cjs:1424:27)

> d = Decimal128.fromStringWithRounding('127341286781293491234791234667890123')
new Decimal128("1.273412867812934912347912346678901E+35")

Double check the following

• Ran npm run check:lint script
• Self-review completed using the steps outlined here
• PR title follows the correct format: type(NODE-xxxx)[!]: description
  • Example: feat(NODE-1234)!: rewriting everything in coffeescript
• Changes are covered by tests
• New TODOs have a related JIRA ticket

[W-A-James]

Link to CI run with pinned npm version