Upgrades to newer version of intl

[mwcbrent]

Caveat: I'm not really much of a dart / flutter engineer so apologies if I broke or removed something that shouldn't be.

This pull request does the following:

• Bumps intl version to 18
• Removes pedantic as it is now deprecated (not sure what to replace this with)
• Adds a helper to the tests. The matchers were getting hung up on a NNBSP character being returned.

Wanted to share if this was at all helpful to anybody else.

[rknell]

Thanks @mwcbrent

I was going to ask why you did what you did but I pulled the code down and checked it, then went down a rabbit hole to find why it broke.

I disagree with the philosophy of the intl guys and changing the whitespace should be a breaking change - as because - it broke our tests and also other peoples code as referenced here: dart-lang/i18n#637. So what I'm going to do is pull down your changes (thank you!) but revert to using the hard coded strings as their attitude towards breaking code worries me and I would like to know about changes in their API going forward even if its just whitespace.

[rknell]

Hey @mwcbrent - I also want to add though, I really appreciate the way you went about making the pull request and not just changing the text in the test to "make it work". Your dart engineering is great.