Don't fail builds when using require() for Lua standard library files

[britzl]

Is your feature request related to a problem? Please describe (REQUIRED):
The build process picks up all calls to require() to detect which files that are required by the engine to make sure they are included in the application build. This can sometimes be a problem when using code from third-parties that are calling require() on Lua language namespaces such as "debug", "string" and "math" or for that matter calling require for commonly used Lua extensions such as "socket" or "lfs".

Describe the solution you'd like (REQUIRED):
Defold should still search for all calls to require() and include any Lua files matching these calls. Defold should however not fail a build if a file is missing. This should at most generate a warning.

Describe alternatives you've considered (REQUIRED):
It is sometimes possible to modify the third-party code that calls require() on a module, but it is not always convenient.

Additional context (OPTIONAL):
Most recent discussion around this: https://forum.defold.com/t/defold-1-2-180-has-been-released/67743/61?u=britzl

[britzl]

This issue definitely poses a problem to users that include third-party Lua modules where it is not uncommon to see things such as:

local debug = require("debug")

It is not always the case that the Lua debug namespace is loaded from the start and you may in other engines or Lua integrations actually have to require it to load it.

We do not wish to force users to make a copy of the code and remove the require() call and we also do not want our users to add a debug.lua in the root of the project just to satisfy our build pipeline.

For commonly used Lua modules such as "socket" and "lfs" it is also common to see code that does require("socket).

In the cases above we may wish to ignore the missing require. But do we really want this in other scenarios for game related code. Example:

local enemy = require("game.enmy") 

What if this is a typo and it should actually read "game.enemy"? Letting that through and only logging a warning is not great either.