clisqlshell: new infrastructure for describe commands

Release note (cli change): The SQL shell (`cockroach sql`, `demo`) now
supports the client-side commands `\l`, `\dn`, `\d`, `\di`, `\dm`,
`\ds`, `\dt`, `\dv`, `\dC`, `\dT`, `\dd`, `\dg`, `\du` and `\dd` in a
way similar to `psql`, including the modifier flags `S` and `+`, for
convenience for users migrating from PostgreSQL.

A notable difference is that when a pattern argument is specified, it
should use the SQL "LIKE" syntax (with `%` representing the wildcard
character) instead of PostgreSQL's glob-like syntax (with `*`
representing wildcards).

Co-authored-by: Nathan VanBenschoten <[email protected]>

pkg/cli/clisqlshell/BUILD.bazel

@@ -7,6 +7,7 @@ go_library(
         "api.go",
         "complete.go",
         "context.go",
+        "describe.go",
         "doc.go",
         "editor.go",
         "editor_bimodal.go",
@@ -51,6 +52,7 @@ go_test(
     name = "clisqlshell_test",
     srcs = [
         "complete_test.go",
+        "describe_test.go",
         "editor_bubbline_test.go",
         "main_test.go",
         "sql_internal_test.go",