* feat(lua): vim.tbl_contains supports general tables and predicates
Problem: `vim.tbl_contains` only works for list-like tables (integer
keys without gaps) and primitive values (in particular, not for nested
tables).
Solution: Rename `vim.tbl_contains` to `vim.list_contains` and add new
`vim.tbl_contains` that works for general tables and optionally allows
`value` to be a predicate function that is checked for every key.
This fixes the following bugs:
`${1:else_text}` -> format with if_text: "else_text"
`${1:-else_text}` -> format with if_text: "else_text"
`${1:}` in `format` (eg. empty else_text) -> error.
`${1:}` (eg. empty placeholder) -> error.
Thanks hrsh7th :)
