Clean up query translator/expression namespace and file placement

[roji]

#33755 moved query translator into their own folder, and with the namespace was e.g. Microsoft.EntityFrameworkCore.Cosmos.Query.Internal.Translators; but our analyzer identifies internal namespaces as ending with Internal. Since the main idea here was file placement, I just changed the namespace back to Microsoft.EntityFrameworkCore.Cosmos.Query.Internal (sorry for the churn).

Also did the same with all expression inside provider projects - they're now grouped under their own directories, but keeping the general Microsoft.EntityFrameworkCore.Cosmos.Query.Internal namespace.

Relational is unfortunately a bit of a mess; some expressions are already grouped under an SqlExpressions directory - although many expressions there don't extend SqlExpression (e.g. SelectExpression). Some other expressions are at the query root instead :( Changing namespaces here would be a breaking change; we can still move the files instead just for cleanliness but keep the namespace (or maybe there's some classification system here I didn't notice, @maumar).

[maumar]

I think the idea behind putting some expressions outside SqlExpressions directory is that those should be "shaper" expressions, rather than sql query (CollectionResultExpression, StructuralTypeProjectionExpression, JsonQueryExpression) - but note how JsonScalarExpression shows up in sql, so it's in the directory.

I do agree that TableExpressionBase -derived expressions in a bit weird. They do describe SQL query though, so maybe that's why.

[roji]

I think the idea behind putting some expressions outside SqlExpressions directory is that those should be "shaper" expressions, rather than sql query

Yeah, that looks like it - though I think we're not totally consistent... In any case, we can think about cleanup at some point...