v15: improve Spelling rule filters by using word boundaries

By using regex word boundary (\b) delimiters, the spelling rule
applies to individual words rather than a word that might contain the
regex filter. For example, `\b[cC]he\b` will match only "che" and "Che"
rather than a regex filter without word boundary delimiters, for
example, `[cC]he` that would match misspelled words that contain the
regex, such as "aache" or "chemitsry".

This commit also combines multiple related filters that share a common
word base, for example, a single filter `"[bB]reakpoint(s)?` rather than
`[bB]reakpoint` and `[bB]reakpoints`.