Make color & font collection initializers public

[johnxnguyen]

What's in this PR?

A small fix for #182

Issues

The initializers for StaticColorCollection and StaticFontCollection are not publicly accessible, thus their properties could not be set.

Causes

The generated memberwise struct initializer is internal by default, even if the struct has public access.

Solutions

Explicitly define public memberwise initializers with default values.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@0095468). Click here to learn what that means.
The diff coverage is 0%.

@@            Coverage Diff            @@
##             master     #184   +/-   ##
=========================================
  Coverage          ?   35.98%           
=========================================
  Files             ?       54           
  Lines             ?     1070           
  Branches          ?        0           
=========================================
  Hits              ?      385           
  Misses            ?      685           
  Partials          ?        0

Impacted Files	Coverage Δ
...Styling/Attribute Collections/FontCollection.swift	0% <0%> (ø)
...tyling/Attribute Collections/ColorCollection.swift	0% <0%> (ø)

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[iwasrobbed]

Thanks @johnxnguyen !