Add fxAddShadow with custom DX texture support

[Xenius97]

Summary

This PR adds the client-side fxAddShadow Lua function by porting PR #4559.

The implementation originates from work by CrosRoad95 in PR #1003. After the original code was abandoned, it was reassembled and modernized in PR #4559, with known crashes and stability issues addressed.

This version extends that work further by allowing the first argument to be either a built-in shadow name or a live 2D DX texture element:

bool fxAddShadow(
    texture,
    x, y, z,
    frontX, frontY,
    sideX, sideY,
    color,
    shadowType,
    zDistance,
    drawOnWater,
    drawOnBuildings
)

Position and offset arguments may also be passed as Vector3 and Vector2 values. The function is client-side only and is also available through the Effect.createShadow OOP alias.

The supported built-in textures are:

car, ped, heli, bike, rcbaron, explosion,
headlight1, headlight2, blood, handman, wincrack, lamp

Custom textures may be created with dxCreateTexture. Two-dimensional render targets and screen sources are also supported.

Each call queues a shadow for one GTA render pass, so fxAddShadow must be called every frame, preferably from onClientPreRender. The queue shares GTA’s native 48-shadow limit and retains its own GPU reference until rendering completes.

https://imgur.com/l5s9lYC

Motivation

The original implementation provides a useful way for Lua resources to access GTA: San Andreas’ projected-shadow system, but it was never merged and was eventually left behind.

This PR brings the modernized implementation into the client while preserving the fixes from the previous work. Support for custom DX textures expands its use beyond GTA’s built-in shadows, allowing resources to render custom transparent masks, projected lighting, and similar world effects without requiring separate geometry.

Test plan

fx-shadow-test.zip

Checklist

• Your code should follow the coding guidelines.
• Smaller pull requests are easier to review. If your pull request is beefy, your pull request should be reviewable commit-by-commit.

[FileEX]

What about #1003 (comment)?

[Xenius97]

What about #1003 (comment)?

I've used for long hours without any issues, no crashes.