Code golf preact.js.gz size down by 53 B ⛳️

[jviide]

This pull request applies a bunch of small code modifications that seem to reduce the overall bundle size. Here's a rough outline of the changes:

• 276850e, 5e78b34, 37ce351, 07b42de mostly move around loop invariants to compress the code.
• 3ec3829, d32aa17, 82f4cca reuse local variables etc. to avoid repetition.
• 3f71109 replaces an Array#map call with Array#some that:
  1. should be just as supported as Array#map but doesn't collect all callback results to an array like Array#map
  2. seems to compress better than Array#forEach
• 76529b7 reorganizes createContext extensively, getting rid of local variable and function declarations.
• 7e53dd2 removes a superfluous check from diffProps - newProps's falsyness is checked although that shouldn't be possible at that point.
• 04646b6 doesn't explictly init isNew to false, as its default undefined value is sufficient.
• The rest of the commits mostly reorder code or modify if (x!=null) checks to if (x) when appropriate.

The performance seems to stay on the same level with master. I used Chrome 74, MacOS 10.14.4 and https://github.com/mathieuancelin/js-repaint-perfs for testing, so YMMV.

The size impact compared to the master is:

bundle file	master	random-opts	delta
preact.js.gz	3548 B	3495 B	-53 B
preact.js.br	3242 B	3201 B	-41 B
preact.module.js.gz	3566 B	3517 B	-49 B
preact.module.js.br	3265 B	3224 B	-41 B
preact.umd.js.gz	3604 B	3561 B	-43 B
preact.umd.js.br	3293 B	3255 B	-38 B

[JoviDeCroock]

All I can say is Wow :D

[marvinhagemeister]

This PR is just... holy moly! I'd love to have @developit take a look at .some() vs the for loops. In my microbenchmarks (I may be doing them wrong) they are faster, but our lord of the benches can likely clear that one up :)

[coveralls]

Coverage remained the same at 100.0% when pulling fa52fc6 on jviide:random-opts into dc4ad8d on developit:master.

[jviide]

Rebased the code on master, removed a couple of commits that used Array#some to replace for-loops (they seemed to bring down the performance a bit). Updated the pull request description accordingly.

[kristoferbaxter]

Accidentally closed from mobile GitHub. Sorry!

[marvinhagemeister]

The benches were settled in slack 🥇 💯 This PR is really awesome! Starting from the detailed commits, to all the benches and all. It's just on a whole other level 👍 👍