Support for template source file introspection

Create a function that allows introspection of the bicep template source file, returning details such as filename and hash. The values would become string literals in the compiled ARM template. These can be used for source traceability. Example:

```
resource contosoZone 'Microsoft.Network/privateDnsZones@2020-06-01' = {
name: 'contoso.com'
tags: {
SourcePath: file().path // /src/modules/dns/contosozone.bicep
SourceFile: file().name // contosozone.bicep
SourceHash: file().hash // 365d36e5599ac9cef725cd93defe6966f2bb16a76fe67cfb4a09f023c64255e1
}
}
```

No files, tests, or entry points are named. Start by locating how Bicep functions are handled and how compiled ARM templates receive string literals. Done means a template source introspection function exposes the filename, path, and hash values shown in the example for source traceability.

Written by the indexing model from the issue text.