feat(text-field): Added support for text field without label

[abhiomkar]

Features included:

• Adds support for text field without label by making floating label element optional for all text field variants.
• Adds support for placeholder with or without floating label element where placeholder is visible only on focused state for text field that has label.

Fixes #4239

Screenshot:

[kfranqueiro]

This seems pretty reasonable, but I'd like us to run it by our designers for review before merging.

[kfranqueiro]

golden.json also needs updating.

[mdc-web-bot]

🤖 Beep boop!

Screenshot test report 🚦

19 screenshots changed from master on commit 1cae66f:

• https://storage.googleapis.com/mdc-web-screenshot-tests/travis/2019/01/28/23_28_46_768/report/report.html?utm_source=github&utm_medium=pr_comment

Details

19 Added:

• spec/mdc-textfield/classes/baseline-placeholder.html

• spec/mdc-textfield/classes/baseline-without-label.html

• spec/mdc-textfield/classes/focused-baseline-placeholder.html

• spec/mdc-textfield/classes/focused-outlined-placeholder.html

• spec/mdc-textfield/classes/textarea-without-label.html

[abhiomkar]

Updated golden screenshots.

[kfranqueiro]

LGTM once goldens are updated for the last changes

[mdc-web-bot]

🤖 Beep boop!

Screenshot test report 🚦

15 screenshots changed from master on commit d8e3f5a:

• https://storage.googleapis.com/mdc-web-screenshot-tests/travis/2019/01/29/16_45_26_950/report/report.html?utm_source=github&utm_medium=pr_comment

Details

15 Added:

• spec/mdc-textfield/classes/baseline-placeholder.html

• spec/mdc-textfield/classes/baseline-without-label.html

• spec/mdc-textfield/classes/focused-placeholder.html

• spec/mdc-textfield/classes/textarea-without-label.html