Rename text-field to text

[lucaswoj]

From @1ec5 on January 5, 2017 10:58

The text-field property should be renamed to simply text.

The name text-field makes it sound like the property was originally intended to identify a field in the feature’s properties object. That happens to be what this property is usually used for, but by that logic we’d have icon-image-field instead of icon-image. Given the enthusiasm for supporting more expressive values for this property in #104 and #47, the word “field” feels downright anachronistic.

The name text-field is also misleading when incorporated into the iOS and macOS SDKs: the developer would expect a textField property to hold an NSTextField or UITextField, or at least some kind of editable control, but not an NSString. There is such a thing as NSText on macOS, but no one ever uses it directly. On the other hand, UILabel.text, analogous to the text-field layout property, is one of the most commonly used properties on iOS.

/cc @lucaswoj @jfirebaugh

Copied from original issue: mapbox/mapbox-gl-style-spec#646

[lucaswoj]

This fits nicely with #218

[jfirebaugh]

Closing here; see #6584.