Fix bug causing increment/decrement issues for some number formats

[jkillian]

What this PR does / why we need it:
When incrementing or decrementing a number, the NumericString.parse class is used to parse strings in to numbers of various formats. However, it used global (stateful) regexes to do this, which meant that funky things could happen after the first call to the method. This PR fixes the issue by simply removing the g flag from some regexes.

This fixes issues, for example, where pressing <C-a> on certain numbers more than once lead to numeric prefixes getting stripped or other odd behavior.

Which issue(s) this PR fixes
Fixes #3545

Special notes for your reviewer:
@Chillee added the g flag in #1721. I think the rest of the logic in that PR still works correctly without the g flags, but feel free to take a look and verify that this change is safe.

[J-Fields]

Thanks!