Allow at least one constant instead of two in any() filter function

[bkoelman]

It turns out that EF Core 6 (tested with PostgreSQL and Sqlite) is smart enough to translate a single-element collection to a SQL = expression, instead of IN (...):

.Where((FilterableResource filterableResource) => #List<string>.Contains(filterableResource.SomeString))
.OrderBy((FilterableResource filterableResource) => filterableResource.Id)
.Take(Tuple.Create(10).Item1)

Multiple elements for #List<string> reference:

-- Executed DbCommand (2ms) [Parameters=[@__Create_Item1_0='10'], CommandType='Text', CommandTimeout='30']
SELECT f.*
FROM "FilterableResources" AS f
WHERE f."SomeString" IN ('four', 'three', 'one', 'two', 'five')
ORDER BY f."Id"
LIMIT @__Create_Item1_0

Single element:

-- Executed DbCommand (1ms) [Parameters=[@__Create_Item1_0='10'], CommandType='Text', CommandTimeout='30']
SELECT f.*
FROM "FilterableResources" AS f
WHERE f."SomeString" = 'yes'
ORDER BY f."Id"
LIMIT @__Create_Item1_0

Closes #1152.

QUALITY CHECKLIST

• Changes implemented in code
• Complies with our contributing guidelines
• Adapted tests
• Documentation updated

[codecov]

Codecov Report

Merging #1234 (faaba0b) into master (84d01c3) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1234   +/-   ##
=======================================
  Coverage   92.62%   92.63%           
=======================================
  Files         243      243           
  Lines        7799     7794    -5     
=======================================
- Hits         7224     7220    -4     
+ Misses        575      574    -1     

Impacted Files	Coverage Δ
...otNetCore/Queries/Internal/Parsing/FilterParser.cs	98.35% <ø> (-0.03%)	⬇️
...ApiDotNetCore/Queries/Expressions/AnyExpression.cs	73.33% <100.00%> (+1.45%)	⬆️

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