Interpolated strings should recognize constants

The usage of interpolated strings should recognize const strings.
The lines underneath should produce the same effect.

Private Const ASTRING As String = "FOO"

Console.WriteLine($"{ASTRING}BAR")
Console.WriteLine(ASTRING & "BAR")

Now the first line translates to an unnecessary string.format

IL_0000: ldstr "{0}BAR"
IL_0005: ldstr "FOO"
IL_000a: call string [mscorlib]System.String::Format(string, object)
IL_000f: call void [mscorlib]System.Console::WriteLine(string)

The second line does the concatenation at compile time

IL_0014: ldstr "FOOBAR"
IL_0019: call void [mscorlib]System.Console::WriteLine(string)

If the concatenation with constants is done at (pre)compile time before handling the interpolated string, then unneeded string format will automagically dissapear as this line does not produce a string format:

Console.WriteLine($"NOVARS")

results in this IL

IL_001e: ldstr "NOVARS"
IL_0023: call void [mscorlib]System.Console::WriteLine(string)