Query: Adds LINQ Support for FirstOrDefault

[adityasa]

Query: Adds LINQ Support for FirstOrDefault

Description

This change adds LINQ support for Enumerable.FirstOrDefault. At the moment only following overload is supported:
public static TSource? FirstOrDefault<TSource> (this System.Collections.Generic.IEnumerable<TSource> source);

Specifically all of the following overloads are disallowed and suitable error is raised:
public static TSource FirstOrDefault<TSource> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,bool> predicate, TSource defaultValue);
public static TSource FirstOrDefault<TSource> (this System.Collections.Generic.IEnumerable<TSource> source, TSource defaultValue);
public static TSource? FirstOrDefault<TSource> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,bool> predicate);

Since FirstOrDefault logic cannot entirely be expressed SQL query, it is achieved using a combination of SQL query and client side operation. Generated query in this case is of the form SELECT TOP 1 VALUE. CosmosQuery then executes a scalar FirstOrDefault operation on the results returned by the backend for such a query.

For e.g.
LINQ Expression:
getQuery(b) .Select(data => data.Flag) .Where(flag => flag) .FirstOrDefault()
SQL Query:
SELECT TOP 1 VALUE root ["Flag"] FROM root WHERE root ["Flag"]

Type of change

Please delete options that are not relevant.

• [] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• [] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [] This change requires a documentation update

Closing issues

To automatically close an issue: closes #IssueNumber

[sboshra]