Add missing Ordinal to {Starts,Ends}With

[roji]

Fixes #18831. We should also use analyzers (#18870) to make sure it doesn't happen again.

Mystery:

Tried to add a test. But mysteriously, the following yields False, True:

Console.WriteLine("__someName_0".StartsWith("@"));
Thread.CurrentThread.CurrentCulture = CultureInfo.GetCultureInfo("th-TH");
Console.WriteLine("__someName_0".StartsWith("@"));

But the same inside a test returns false for both... There's some environmental thing going on, but don't think it's worth digging into it.

[smitpatel]

Look at EntityType_name_is_stored_culture_invariantly test. We have attribute to set custom culture for test.

[roji]

@smitpatel yeah I tried that, but I can't get this to repro in the tests for some inexplicable reason - only in a console app. Merging as the test value seems a bit low here.