ClangSharpPInvokeGenerator incorrectly handles string escape sequences in preview codegen mode

[DaZombieKiller]

Given the following C/C++ definition:

static const char StringContainingNulls[] = "Hello\0World";

ClangSharpPInvokeGenerator will produce the following C# code with --config preview-codegen:

public static ReadOnlySpan<byte> StringContainingNulls => "Hello\\0World"u8;

Instead of the expected:

public static ReadOnlySpan<byte> StringContainingNulls => "Hello\0World"u8;