Regex: Add slash command input hook

Slash command output for sys and sendas commands were being formatted,
but add the ability for user placement to also apply to slash command
invocations.

Some slash commands will require an output hook, so add exclusions
inside the code itself.

Signed-off-by: kingbri <bdashore3@proton.me>

public/scripts/extensions/regex/engine.js

@@ -11,8 +11,7 @@ const regex_placement = {
     MD_DISPLAY: 0,
     USER_INPUT: 1,
     AI_OUTPUT: 2,
-    SYSTEM: 3,
-    SENDAS: 4
+    SLASH_COMMAND: 3
 }
 
 const regex_replace_strategy = {