Add support for a limited set of expressions to be converted to JS
while creating a view index

Supported expressions

1. field references
2. path expressions (nested fields, array elements), including long path
expressions
3. arithmetic and concatenation operators, including long sequences (e.g. a
+ b + c + d)

4. String Functions
a. Upper
b. Lower
c. Substr
d. Contains
e. length

5. Date functions

a. str_to_millis
b. now_millis

6. Math functions
sin, cos, log etc.

Address MB-12257 partly. Added a mechanism to check whether a bucket has
been deleted as part of the pool.refresh() function
Merge branch 'master' of github.com:couchbaselabs/query