fast-syntax-highlighting highlighting of multi-word abbreviations

[olets]

fast-syntax-highlighting highlighting of single-word abbreviations was done in #24.

Useful links:

• fsh chroma docs: https://github.com/zdharma-continuum/fast-syntax-highlighting/blob/master/CHROMA_GUIDE.adoc
• Initial discussion of how to expand single-word support to multiple words https://github.com/olets/zsh-abbr/issues/24#issuecomment-1546618585