Minecraft – How to add a loot table to an item in a loot table in minecraft

I want to have a minecart with a loot table within the block loot table I am making. I have already started in the process, and I know that I have up to that point formatted corectly, but I don't know the NBT tag formatting for adding the loot table… or if it is even possible in the first place… can someone please help? I am using the most recent 1.14 snapshot but it should be compatible with 1.13 format since that is what I've been using for everything else.

Here is what I have

"functions": [
{
"function": "set_data",
"data": 0
},
{
"function": "set_nbt",
"tag": "{NBT}"
}

I just don't know what to replace NBT with to get what I ask?

I know the loot table I want to use is named "abandoned_mineshaft" and is found under the "chests" default loot tables.

I already tried "{LootTable:\"minecraft:chests/abandoned_mineshaft\"}" (take away the \'s and it is what you use for /summon) for the NBT tag as well as "{BlockEntityTag:{LootTable:\"minecraft:chests/abandoned_mineshaft\"}}" so I don't know where to go next… 

An alternate solution that'd work for what I hope to accomplish is if the data pack could summon the minecart like infested blocks summon silverfish.