Valve left a few things out of their FGD. This brings them back and adds some quality of life improvments.
This used to be the community placeholder FGD before the official workshop came out. You can find that in the legacy branch.
Download latest zip file from master and drop hlvr.fgd and halflife2.fgd into C:\Program Files (x86)\Steam\steamapps\common\Half-Life Alyx\game\hlvr or the relevant location of your Half-Life Alyx install (still within ~\Half-Life Alyx\game\hlvr).