[core] feat(NumericInput): add leftElement prop

[alex-c]

Fixes #5051

Hello, I created this draft PR, as I would like to fix #5051, but I have trouble building the project on Windows (see #4221) and am not sure what I should add in the ways of tests.

• I added the necessary change and added an example to the docs. While I cannot run yarn verify (see above), yarn compile and yarn lint run fine. The change seems to work fine (see screenshot at the bottom).

• I am also not sure what/how much I should do in the ways of tests. So far, there are no tests for NumericInput at all, as far as I can see... Nor are there for InputGroup?

Checklist

• Includes tests
• Update documentation

Changes proposed in this pull request:

Add leftElement as an alternative to leftIcon for NumericInput, the same way it is for InputGroup. Since NumericInput uses InputGroup, the leftElement prop can just be passed down.

Reviewers should focus on:

leftElement should be working for NumericInput.

Screenshot

The following screenshot is from the example I added to the docs. Setting a button with a popover in leftIcon breaks the layout. With leftElement it works fine:

[palantirtech]

Thanks for your interest in palantir/blueprint, @alex-c! Before we can accept your pull request, you need to sign our contributor license agreement - just visit https://cla.palantir.com/ and follow the instructions. Once you sign, I'll automatically update this pull request.

[adidahiya]

Sorry about the trouble building the project in Windows.

Generally I advise running the individual build scripts in each package for the best debugging experience. For example:

cd packages/core
yarn compile
yarn lint
yarn test

It looks like you've managed to trigger the CI build successfully, though, so you should get build & test results here within a few minutes of pushing your commits.

There are actually quite a few tests for NumericInput: https://github.com/palantir/blueprint/blob/develop/packages/core/test/controls/numericInputTests.tsx

I'll review this PR soon!

[alex-c]

Oh, I guess I only looked for tests in the forms directory. I'll take another look and see if I can add some meaningful tests.

[alex-c]

I have now added two basic test cases.

[adidahiya]

docs preview here

nice, this looks great! thanks for the PR, I appreciate the new option added to the NumericInput example in the docs.