Spell checking tool

Introduce a tool to catch spelling and common typing problems, such as "the the", "decomission", etc.

In the meantime, we can use Checkstyle's Regexp pattern, but that's pretty inefficient(?) and may slow down the build.

Inspired by #7154.

Start by reviewing the proposed Checkstyle Regexp pattern and the context in issue #7154. Define how the spelling tool should catch repeated words and misspellings such as “the the” and “decomission,” then verify that the chosen integration catches these cases without slowing the build.

Written by the indexing model from the issue text.