New locking model for single log file in native applications with managed parts

[FreeAndNil]

We have a native application (Delphi) which loads .net dlls at runtime.
With this adjustment we can (optionally) share the log file between the native and the managed part of the application.

@fluffynuts Could you please review?

[fluffynuts]

looks ok to me, tho I'd really prefer string interpolation instead of concatenation - I'll merge in and fix up myself

[FreeAndNil]

fixes #259

[snakefoot]

Just curious how does NoLock work when having two file-handles to the same file ?

Forexample:

• File-handle-1 writes 10 bytes, and moves its file-position 10 byte forward
• File-handle-2 writes 20 bytes and moves its file-position 20 bytes forward

Will File-Handle-2 not overwrite the contents just written by File-Handle-1 ?

With the following code that disables buffering:

 using var fileStream1 = new FileStream(@"C:\Temp\Hello.txt", FileMode.Append, FileAccess.Write, FileShare.ReadWrite, 1, FileOptions.None);
 using var fileStream2 = new FileStream(@"C:\Temp\Hello.txt", FileMode.Append, FileAccess.Write, FileShare.ReadWrite, 1, FileOptions.None);
 fileStream1.Write(System.Text.Encoding.UTF8.GetBytes("Hello"));
 fileStream2.Write(System.Text.Encoding.UTF8.GetBytes("Goodbye World"));
 fileStream1.Write(System.Text.Encoding.UTF8.GetBytes("World"));

Then the contents of the output-file becomes this:

GoodbWorldrld

If enable FileStream with default buffer-size like this:

using var fileStream1 = new FileStream(@"C:\Temp\Hello.txt", FileMode.Append, FileAccess.Write, FileShare.ReadWrite);
using var fileStream2 = new FileStream(@"C:\Temp\Hello.txt", FileMode.Append, FileAccess.Write, FileShare.ReadWrite);
fileStream1.Write(System.Text.Encoding.UTF8.GetBytes("Hello"));
fileStream2.Write(System.Text.Encoding.UTF8.GetBytes("Goodbye World"));
fileStream1.Write(System.Text.Encoding.UTF8.GetBytes("World"));

Then the contents of the output-file becomes this:

HelloWorldrld

How does one ensure that the 2 FileHandles doesn't generate garbled output with NoLock ? (See also #259)