Add custom formater for very small number in Numeral.js

[Angel0r]

Describe the feature:
Numeral.js supports custom formaters but not for very "very" small numbers.

Describe a specific use case for the feature:
Specifically in metric visualisation, kibana cannot show very small numbers, shorter. So for example I want show this number "5.123,123,123,324,234e-53" like "5.123e-53".

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[wylieconlon]

Just confirmed that we don't have formatting support for this, for both negative and positive values. There is already a scientific notation formatter which does not allow control over the number of digits shown:

0,0.0e+0

1.23456789e-15  |  +1.23,456,789e-15
1.99e+22        |  +1.99e+22

0,0e-0

1.23456789e-15  |  1.23,456,789e-15
1.99e+22        |  1.99e+22

I would imagine that we don't want to break existing formatters, so maybe we can add a new formatter for this.

The closest fit to this request might actually be a formatter that accepts a fixed # of digits to show, similar to the numeral-js fork numbro: https://numbrojs.com/format.html

We could build a custom formatter for "Fixed length number" and "Fixed length scientific notation" for example, neither of which requires numeraljs formatting to implement.

The biggest reason to stick with numeraljs is its number locale support. Otherwise, there is built-in JS support for the following operations:

(19900000000000000000000).toFixed(2) -> 1.99e+22
(0.00000000000000123456789).toExponential(2) -> 1.23e-15

[elasticmachine]

Pinging @elastic/kibana-app-arch (Team:AppArch)

[petrklapka]

Thank you for contributing to this issue, however, we are closing this issue due to inactivity as part of a backlog grooming effort. If you believe this feature/bug should still be considered, please reopen with a comment.