What does this PR do?

Adds some truncation to deal with floating point precision issues in javascript.

From the test case shown below, 2.26 + 8.04 === 10.299999999999999 instead of 10.3.

See this post for some details on the underlying shortcomings of javascript: https://stackoverflow.com/questions/1458633/how-to-deal-with-floating-point-number-precision-in-javascript

Where should the reviewer start?

Meter.js

What testing has been done on this PR?

The test scenario from the issue involves:

<Meter
  type="circle"
  values={[{ value: 2.26 }, { value: 8.04 }]}
  max={10.3}
/>

A unit test has been added.

How should this be manually tested?

see ^^^

Do Jest tests follow these best practices?

follows existing test patterns

What are the relevant issues?

#6190

Do the grommet docs need to be updated?

no

Should this PR be mentioned in the release notes?

yes

Is this change backwards compatible or is it a breaking change?

backwards compatible