Add support for disable_coord param to terms query

[keety]

Trivial change to enable disable_coord support for TermsQuery .

Added test case to verify support for options in TermsQuery Parser.

Closes #12755

[jpountz]

Actually I was recently thinking about changing this query so that we always return a TermsQuery. It would break backward compatibility, but I'm not too happy with the current state where terms, when used as a query, is essentially a shortcut for creating a bool query. I would rather make the generated query and filter have more consistent behaviours and recommend to use bool instead of terms if disable_coord and/or min_shoul_match are required?

[clintongormley]

@jpountz i agree with your comment - this should be a simple query. All the terms query buys you is a more compact syntax when looking for lots of terms. I would guess that min_should_match and coord is more useful when dealing with only a few terms, so using a bool query instead would be ok

[jpountz]

Ohhh I understand why you opened this PR now: this used to be supported in 1.x but support for this parameter was accidentally lost in 2.x. So we have a bw compat break. Then I'm inclined to merge the change and to later think about how we could deprecate min_should_match/disable_coord.