Trigram indexes: faster text searching

Feature request: Add a trigram style of index. Implemented correctly, they'll make predicates such as

column LIKE '%string%'

sargable, and make a big difference to performance. Predicates like that show up all over the place in running code – for example the search-box function in WordPress uses them.

I propose syntax like

CREATE INDEX index_name USING TRIGRAM ON tbl(col1,col2);

PostgreSQL has an elaborate extension-based trigram indexing system. Not all that stuff is necessary to get the text search benefits. Writeup here.
https://www.postgresql.org/docs/current/pgtrgm.html