Add support for GAME function and providing gaming inputs at runtime

[chrispcampbell]

A number of developers have requested support in SDEverywhere for Vensim's GAME function and for game mode in general (see Vensim docs here and in their user guide here).

Currently SDEverywhere accepts models that use the GAME function, but it simply returns the input value. Adding proper support for the GAME function will entail changes to the compile and runtime packages. I also plan on adding a simple example app that demonstrates how to use the new API that will allow for providing game inputs at runtime.

[chrispcampbell]

Here's a quick status report. Most of the work on supporting "gaming mode" in SDEverywhere has been in adding the ability for an application to override lookups/data at runtime, and to make that happen there have been a series of improvements made in branches under separate issue numbers.

Completed

• Refactor runtime and runtime-async packages to allocate/grow buffers on demand #471: Refactored the runtime packages to allocate buffers on demand. This was a prerequisite for adding JS code gen and dynamic lookups.
• Add compiler and runtime support for generating pure JS as an alternative to C/Wasm #437 and Update build and plugin packages to support JS code generation #479: Implemented support for JS code gen. This was already mostly complete and had been sitting on a branch. Getting this merged first made it much easier to prototype the new support for dynamic lookups and gaming inputs.

Completed as of June 3 (was: In progress as of May 30)

• Allow for overriding data variables and lookups at runtime #472: Added support for overriding data variables and lookups at runtime. This was about 80% of what's needed to handle gaming inputs that are supplied at runtime. I will merge this branch today.
• Add example that demonstrates how to use GAME function and gaming inputs #489: Added a new house-game example app, based on the house construction model from the Vensim user guide. This is mostly complete as well and can be merged before I finish work on this issue (see next item).

Completed as of August 16 (was: Completing soon)

• Allow for controlling whether the minimal model listing is included in the generated model #503: Added support for opt-in configuration settings for bundling the model listing with the generated model (to allow for finding lookup variables by name at runtime) and for enabling the setLookup function (to allow for providing game inputs at runtime).
• Add support for GAME function and providing gaming inputs at runtime #483 (this issue): Once I've merged the branches for the issues listed above, I will be finishing up the last ~20% of gaming support, which should be straightforward. This entails changing the compiler to transform GAME function calls to read from a Lookup instance, which contains the gaming inputs (basically a lookup table) that the application sets at runtime. Once the compiler changes are complete, I will update the house-game example to show how it all fits together.

[chrispcampbell]

Now that support for the GAME function is implemented in SDEverywhere, it is now possible to implement turn-based games and simulations in your SDEverywhere-based project. See examples/house-game in this repo for a working example.