Guidance on acceptable paths is not discoverable

[jeskew]

First reported by @TheOnlyWei in #15994 (reply in thread)

Anywhere Bicep accepts a path (module and import statements; load*Content functions), it must be a relative path that uses a / directory separator to ensure portability. However, this isn't very discoverable if you start out with an absolute Windows path.

param test string = loadTextContent('C:\<insert home path>\.ssh\id_rsa.pub')

will confusingly report that the value must be a compile time constant. Not sure what causes that, but I think \< confuses the lexer somehow. Using a path with no placeholders:

param test string = loadTextContent('C:\Users\jeskew\.ssh\id_rsa.pub')

will report that the string contains illegal escape sequences. Escaping the backslashes:

param test string = loadTextContent('C:\\Users\\jeskew\\.ssh\\id_rsa.pub')

will report that the string contains an illegal : character. Removing the drive:

param test string = loadTextContent('\\Users\\jeskew\\.ssh\\id_rsa.pub')

will finally report that the / directory separator needs to be used instead of \. Replacing the directory separators:

param test string = loadTextContent('/Users/jeskew/.ssh/id_rsa.pub')

will report that paths need to be relative, not absolute.

That's a lot of iteration! Maybe we should put more guidance in earlier messages or in the load*Content function descriptions.