Subdocument error refactoring and array method renaming (iteration 3)

List to be confirmed from diffing the RFC:

[x] clarify error handling in SDK
(still in PR: https://github.com/couchbaselabs/sdk-rfcs/pull/31)
[x] error change in counter
(merged in the draft, never was a PR?)
https://issues.couchbase.com/browse/MB-18169
https://github.com/couchbaselabs/sdk-rfcs/commit/0926353154adf643272158b268f1302f564ac505#diff-03585585aaf212f6a3f3bc7d8c90d3f0
[x] array method renaming
(issue only: https://github.com/couchbaselabs/sdk-rfcs/issues/28)
[x] check correct implementation of "clarify error values" (https://github.com/couchbaselabs/sdk-rfcs/commit/d7f293fb646253f1de344b41b41e019b23a72c54)

These other changes are part of the 3rd iteration (target version 2.2.6):

• JCBC-938: multiValue support (still in RFC design: https://github.com/couchbaselabs/sdk-rfcs/pull/29)
• JCBC-939: add retrieveIn() at bucket level as a shortcut for multiple gets in a LookupInBuilder
• JCBC-940: builder's Do() method becomes Execute()? (not confirmed in RFC yet)