Deprecate and add migrator for top level named classes

[DylanPiercey]

Description

Adds a deprecation and migration for named top level classes.

class x {
}

<div/>

becomes:

class {
}

<div/>

Checklist:

• I have read the CONTRIBUTING document and have signed (or will sign) the CLA.
• I have updated/added documentation affected by my changes.
• I have added tests to cover my changes.

[codecov]

Codecov Report

Merging #1372 into master will decrease coverage by <.01%.
The diff coverage is 92.85%.

@@            Coverage Diff             @@
##           master    #1372      +/-   ##
==========================================
- Coverage   90.59%   90.58%   -0.01%     
==========================================
  Files         341      343       +2     
  Lines       12467    12476       +9     
==========================================
+ Hits        11294    11302       +8     
- Misses       1173     1174       +1

Impacted Files	Coverage Δ
src/core-tags/components/class-tag-transformer.js	100% <100%> (ø)
src/core-tags/components/class-tag-node-factory.js	100% <100%> (ø)
src/core-tags/migrate/class-tag.js	87.5% <87.5%> (ø)

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[coveralls]

Coverage decreased (-0.001%) to 90.59% when pulling 6d70aa1 on migrate-top-level-named-class into 535daf9 on master.