[MC-186857] "/datapack disable" shows success message after a data pack is disabled rather than after it is run, causing inconsistencies with "/datapack enable"

The bug

When using /datapack disable to disable a data pack, the "Disabled data pack" message is not shown after the command is run but instead after the data pack is successfully disabled. This is inconsistent with /datapack enable as it shows the "Enabled data pack" message right after it is used. This is not the case in 20w21a and previous snapshots.

If it is intended, then /datapack enable should show its success message after a data pack is successfully enabled to be consistent with /datapack disable. However, it would be strange especially with functions in load.json that have /say or other similar commands.

Causes

This might be caused by the new loading changes with data packs.

How to reproduce

Use the following command to enable command output:
```
/gamerule sendCommandFeedback false
```
Use /datapack enable to enable a data pack.
→ The "Enabled data pack" message is shown after the command is run.
Use /datapack disable to disable the data pack.
→ The "Disabled data pack" message is shown after the data pack is disabled.