[TextField] Fix first character composition issue

[keifuji]

• PR has tests / docs demo, and is linted.
• Commit and PR titles begin with [ComponentName], and are in imperative form: "[Component] Fix leaky abstraction".

Tiny change. It seems to me that, when the component is conrolled,
'value' needs to be checked only in componentWillReceiveProps,
and event.target.value in handleInputChange has nothing to do with
hasValue state.

At least, this PR can fix #3394 issue which, still remaining despite #5540,
breaks 'first' character composition of CJK or other input methods
when used with, for example, redux-form.

Closes #3394.

[oliviertassinari]

@keifuji The idea behind that change looks good to me. Would you mind adding a test in case it's introducing a regression and we need to do further work? Thanks for the fix!

[keifuji]

@oliviertassinari I added some tests to check hasValue state regarding event and value prop.
(I'm not familiar with enzyme, so it might be odd.)

Anyway, I found the problem has the same origin as inconsistency between state.hasValue and props.value. In fact, the question is not re-rendering but pre-rendering before it receives next props. Until then, the state rest true even though props.value is still invalid.

These are logs from TextField wrapped by reduxForm:

1. handleInputChange -----------------------------------
   states and props: {this.props.value: "", hasValue: false}
   reduxForm.onChange {firstName: "a"}
   ** render TextField ** // unnecessary rendering triggered by setState
2. componentWillReceiveProps ---------------------------
   states and props: {this.props.value: "", hasValue: true} // <==== Inconsistency!
   componentWillReceiveProps {nextProps: Object, value: "a"}
   ** render TextField ** // reasonable rendering
   (callback) setState in componentWillReceiveProps: {this.props.value: "a", isValid: true, hasValue: true}
   (callback) setState in handleInputChange: {this.props.value: "a", isValid: true, hasValue: true}

So I included additional tests for controlled component, which will be able to prevent the issue from reappearing, and necessarily fails in the current version.

[mbrookes]

@keifuji Thanks!