Sqlite: Support uninitialized EXPLAIN queries

[AlexanderTaeschner]

We ignore now when paramters are not initialized in case a EXPLAIN query is used.

Fixes #16647

[bricelam]

Blocked on ericsink/SQLitePCL.raw#328

[AlexanderTaeschner]

My local build shows that the corresponding tests in Microsoft.Data.Sqlite.winsqlite3.Tests fail with an exception: System.EntryPointNotFoundException : Unable to find an entry point named 'sqlite3_stmt_isexplain' in DLL 'winsqlite3'. Should I guard the use of sqlite3_stmt_isexplain with a try ... catch(EntryPointNotFoundException) and use the text comparison if this occurs?

[bricelam]

No text comparison. Maybe something like this:

if (sqlite3_libversion_number() < 3028000
    || sqlite3_stmt_isexplain(stmt) == 0)
{
    // throw missing parameters
}

[bricelam]

Or better yet, just change the assertion:

if (new Version(connection.ServerVersion) < new Version(3, 28, 0))
{
    Assert.Throws<InvlidOperationException>(
        () => command.ExecuteScalar()));
}
else
{
    Assert.NotNull(command.ExecuteScalar());
}

[bricelam]

(Rebased on master and squashed)

[bricelam]

Thanks, @AlexanderTaeschner!