Add new trace flags

[justgo97]

This will allow distinguishing different trace types easily, For example an efficient method to make bullets penetrate through teammates would be:

#include <amxmodx>
#include <fakemeta>
#include <reapi>

// Custom flags that we can retrieve in pfnShouldCollide
// Starting from BIT(16) to reserve space for more flags for Engine
#define FTRACE_BULLET				(1<<16)
#define FTRACE_FLASH				(1<<17)

public plugin_init() {
    register_plugin("Bullets penetrate teammates", "0.0.1", "JustGo")

    register_forward(FM_ShouldCollide, "FMHook_ShouldCollide")
    register_forward(FM_AddToFullPack, "FMHook_AddToFullPack_Post", 1)
}

public FMHook_ShouldCollide(entTouched, entOther) {
    if(!is_user_alive(entTouched) || !is_user_alive(entOther)) return FMRES_IGNORED

    if((global_get(glb_trace_flags) & FTRACE_BULLET) && isSameTeam(entTouched, entOther)) {
        forward_return(FMV_CELL, 0)
        return FMRES_SUPERCEDE
    }

    return FMRES_IGNORED
}

public FMHook_AddToFullPack_Post(es_handle,e,ent,host,hostflags,player,pSet)
{
    if(!player) return FMRES_IGNORED;

    if(!is_user_alive(host) || !is_user_alive(ent)) return FMRES_IGNORED

    if(isSameTeam(host, ent))
    {
        set_es(es_handle, ES_RenderMode, kRenderTransAlpha)
        set_es(es_handle, ES_RenderAmt, 100 );
    }
    return FMRES_IGNORED;
}

stock isSameTeam(id1, id2) {
    return (get_member(id1, m_iTeam) == get_member(id2, m_iTeam))
}

Also now it would be possible to create an entity that is both shootable and can be trespassed:

public FMHook_ShouldCollide(entTouched, entOther) {

    ...
    
    if(!isCustomEntity(entTouched)) return FMRES_IGNORED

    if(!(global_get(glb_trace_flags) & FTRACE_BULLET)) {
        forward_return(FMV_CELL, 0)
        return FMRES_SUPERCEDE
    }

    return FMRES_IGNORED
}