Better cast/convert support for Cosmos

[ChrisJollyAU]

Improve the support and handling of the cast/converts in Cosmos

Originally started for #34963 but after #34982 was created extended that work to more cases

VisitUnary now leaves the Convert operation in place instead of stripping it. This has 2 potential benefits:

• Similarity between Cosmos and relational may help any efforts to create a common shared base rather than a lot of duplication of things (e.g. SqlExpressionFactory etc) in Cosmos
• Leaving it in place allows binary expressions to work out what type mapping the Convert needs (if it doesn't have one already)
• This is especially the case with string concatenation to an int or something like that. the int value will have a Convert to type of Object - aka we know we need a convert but we don't yet know what to convert it to. The type mapping handling of the binary expression will work it out and apply to all sides

In the QuerySqlGenerator, we effectively no-op most casts except for if we have a convert to string.

This does light up a number of math function tests that were failing - all of them due to #17246 (client evaluation exception)
Also some tests for #20677 are now passing (not all of them related to that issue)
The Cosmos tests for #34729 are now passing as well

This fixes #34982