Add _opts property type in Ajv.Ajv

[b4h0-c4t]

What issue does this pull request resolve?
resolve #1253 issue.

What changes did you make?
Add type declaration Ajv.Ajv._opt

Is there anything that requires more attention while reviewing?
The reason why I set any type is other any object( ex. _metaOpts ) could not compatible with detailed objects.

[epoberezkin]

Shouldn’t it be the same interface as for Options?

[b4h0-c4t]

@epoberezkin
Thanks for your review.
I think Options do not have some x._opts properties. (e.x. defaultMeta)

[b4h0-c4t]

Self-resolved.
defaultMeta can translated meta.

[epoberezkin]

I am thinking it may be best to wait a bit until v7 is released in a week or so...

[epoberezkin]

It might be important to access this property though - defaultMeta is not the same as meta, so it should be added too.

Merging it.

[alasdairhurst]

@epoberezkin @b4h0-c4t is defaultMeta intended to be accessed exclusively via ajv._opts or is it available to be set in the constructor as part of the public API?

right now it's undocumented and i don't see any recommendation for using it other than from the old v5 docs, but it seems to work if you set it in the constructor as long as you add the relevant metaSchema straight afterwards. Maybe i'm missing something important though.