[morley-debugger#10] Fix debugger cursor jumping on extra instructions

Description

Currently, when type-checking the STACKTYPE and FN extra instructions, two problems occur (with their solutions):

1. • Problem: STACKTYPE is converted to a Nop, which may include a WithLoc as well. It's bizarre and confuses the debugger.
   • Solution: Add STACKTYPE typed ExtInstr. Patch the type-checker to include such instruction.
2. • Problem: FN is inlined in the code block and its WithLoc meta-instructions will point at the typed stack function definition, with no reference to its usage site.
   • Solution: Add typed Fn meta-instruction. Patch the type-checker to include such instruction and add a WithLoc when producing such instruction as well.

See also: morley-debugger!14 (merged)

Related issue(s)

Pre-requisite to solve morley-debugger#10 (closed)

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