Improve syntax highlighting for class members

[JackKenney]

Two requests for improving the PHP syntax highlighting in ZED:

1. The highlight.scm seems to pick up the constant variable CONST on this class as @constructor highlights, instead of @constant highlights.
2. The highlight.scm correctly respects usages of the ->property accessing (cyan), and ->function calling (blue), but highlights the definition of the property protected int $default = 1000; with the @variable coloring instead of the @property coloring.

Relevant syntax snippet:

          "constant": {
            "color": "#B310A5"
          },
          "constant.builtin": {
            "color": "#B310A5"
          },
          "constructor": {
            "color": "#B00F0F"
          },
          "keyword": {
            "color": "#875B10"
          },
          "number": {
            "color": "#B310A5"
          },
          "primary": {
            "color": "#002b36"
          },
          "property": {
            "color": "#037585"
          },
          "punctuation": {
            "color": "#002b36"
          },
          "punctuation.bracket": {
            "color": "#875B10"
          },
          "type": {
            "color": "#795CA5"
          },
          "variable": {
            "color": "#102530"
          },