Deduplicate HTMLBars / Handlebars Helper tests.

Finishes what was started in #9529.
Merge pull request #9532 from rwjblue/dedup-helper-tests

Deduplicate HTMLBars / Handlebars Helper tests.
[DOC] Grammar tweaks on computed property docs.
Merge pull request #9540 from markstory/computed-prop-docs

[DOC] Grammar tweaks on computed property docs.
Use embedded Handlebars version for HTMLBars compiler.
Merge pull request #9539 from rwjblue/build-stuff

Use embedded Handlebars version for HTMLBars compiler.
Fix version constraint in composer.json
Merge pull request #9544 from aminin/master

Fix version constraint in composer.json