EuiFieldText: converted to Typescript

[ffknob]

Summary

Closes #2648

Converted EuiFieldText to Typescript.

Checklist

• Check against all themes for compatability in both light and dark modes
• Checked in mobile
• Checked in IE11 and Firefox
• Props have proper autodocs
• Added documentation examples
• Added or updated jest tests
• Checked for breaking changes and labeled appropriately
• Checked for accessibility including keyboard-only and screenreader modes
• A changelog entry exists and is marked appropriately

[elasticmachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?

[ffknob]

Just one thing: I had to deal with ./components/color_picker/color_picker.tsx:346:17 trying to pass a ReactChild to the aria-label property (see error below). I really don't know if my fix is the way to go or no...

src/components/color_picker/color_picker.tsx:346:17 - error TS2322: Type 'ReactChild' is not assignable to type 'string | undefined'.
  Type 'number' is not assignable to type 'string | undefined'.

346                 aria-label={isColorSelectorShown ? openLabel : closeLabel}

[chandlerprall]

Also needs:

• remove src/components/form/field_text/index.d.ts
• remove reference at

  eui/src/components/form/index.d.ts

  Line 5 in 705de53

  /// <reference path="./field_text/index.d.ts" />

[chandlerprall]

Lastly, needs to touch a couple more files,

• remove src/components/form/field_text/index.d.ts
• remove reference at

  eui/src/components/form/index.d.ts

  Line 5 in 705de53

  /// <reference path="./field_text/index.d.ts" />

then this should be good to go

[ffknob]

Had to commit skiping pre-commit hook. Couldn't find a way to get pass this error (don't know where it came from, since I just commited without any problems):

pre-commit: 
pre-commit: We've failed to pass the specified git pre-commit hooks as the `test-staged`
pre-commit: hook returned an exit code (1). If you're feeling adventurous you can
pre-commit: skip the git pre-commit hooks by adding the following flags to your commit:
pre-commit: 
pre-commit:   git commit -n (or --no-verify)
pre-commit: 
pre-commit: This is ill-advised since the commit is broken.
pre-commit: 

[chandlerprall]

Changes LGTM, pulled & tested locally

[chandlerprall]

jenkins test this

[chandlerprall]

Had to commit skiping pre-commit hook. Couldn't find a way to get pass this error (don't know where it came from, since I just commited without any problems):

Hmm, interesting. I checked out your branch out and don't see any issues (CI passed as well). If you continue getting this on other branches please bring it up again.