Move Day.js plugin types import to global typings

[lhsazevedo]

Fixes #2417

Changes proposed in this pull request:
Remove Day.js relativeTime plugin types import from humanTime util and add it to the global typings file.
See @davwheat's proposal on #2417.

Reviewers should focus on:
Ensuring that no error occurs when compiling the humanTime util.

$ ./node_modules/.bin/tsc --esModuleInterop ./@types/global/index.d.ts ./src/common/utils/humanTime.ts

Note that you'll need to pass the --esModuleInterop to avoid the following error (unrelated to this PR):

node_modules/dayjs/index.d.ts:3:1
    3 export = dayjs;
      ~~~~~~~~~~~~~~~
    This module is declared with using 'export =', and can only be used with a default import when using the 'esModuleInterop' flag.

This flag is highly recommended by the TypeScript team for both new and existing projects. I didn't add it to tsconfig.json because I don't understand ts enough right now to guarantee that it won't break anything :)

[davwheat]

This flag is highly recommended by the TypeScript team for both new and existing projects. I didn't add it to tsconfig.json because I don't understand ts enough right now to guarantee that it won't break anything :)

Great spot. I'll update the tsconfig repo now.

Actually, this flag is already part of our tsconfig repository, which core inherits from. It's weird that running tsc didn't pick it up... 🤔

[davwheat]

Looks good to me.

Running ./node_modules/.bin/tsc.cmd --esModuleInterop ./src/common/utils/humanTime.ts seems to work. (Specifying the typings file in global isn't needed because it's included by the tsconfig. No errors when doing so.

[lhsazevedo]

Great, thanks for reviewing!

[dsevillamartin]

Not tested locally, changes make sense though.