[v4] [icons] fix: pre-es2017 compatibility

[gluxon]

Fixes #5097

Changes proposed in this pull request:

Switches an Object.values usage to a for ... in ... loop for pre-es2017 browser compatibility.

Reviewers should focus on:

Edit: The guard-for-in ESLint rule triggered on the below. Updated the commit for propertyIsEnumerable.

According to MDN, Object.values also filters on own enumerable properties, so technically we should also check for Object.prototype.propertyIsEnumerable().

TypeScript doesn't seem to generate non-own enumerable properties for enum objects though, so in practice the extra check isn't needed. https://www.typescriptlang.org/play?#code/KYOwrgtgBAYg9nKBvAsAKCpqAhAhgJygF4oAiAIwNPQF910AzOQgCgGM4QBnAFygGtgATygBLELAQBKZOixQO3OABtgAOmVwA5i0FCptIA

Happy to add it if reviewers think the extra soundness is worthwhile.

[palantirtech]

Thanks for your interest in palantir/blueprint, @gluxon! 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.

[gluxon]

Did a quick smoke test to make sure this didn't affect the contents of IconNames.

❯ cd packages/icons

# Before
❯ git reset --hard ORIG_HEAD
HEAD is now at 4dac1637 Publish
❯ node -e 'console.log(Object.keys(require("./lib/cjs/iconNames").IconNames).length)'
1078
❯ node -e 'console.log(require("./lib/cjs/iconNames"))' | md5sum
8cb0237c9ed0ff2db4679aed00f76a00  -

# After
❯ git reset --hard ORIG_HEAD
HEAD is now at 1bcd43e7 [v4] [icons] fix: pre-es2017 compatibility
❯ yarn compile  
❯ node -e 'console.log(Object.keys(require("./lib/cjs/iconNames").IconNames).length)'
1078
❯ node -e 'console.log(require("./lib/cjs/iconNames"))' | md5sum
8cb0237c9ed0ff2db4679aed00f76a00  -

[adidahiya]

Since we already require a few modern language features to use Blueprint (including a few which are not fully supported in IE11 and thus require polyfills), I'd rather take a different approach.

Rather than add backwards-compatible code for IE11, let's instead update the docs to indicate that Object.values() support is now required at runtime with Blueprint v4.0. Users can polyfill it with core-js.

We are planning to completely remove support for IE11 anyway soon (I'll add a deprecation notice to the docs before the v4.0 stable release).

[gluxon]

Sounds good to me. Thanks for taking a look @adidahiya. 🙂