#4120 PIC16: emit COFF type and array debug metadata with --debug-xtra

[zeynelsagcan]

This patch adds Microchip COFF type metadata for the PIC16 backend when --debug-xtra is enabled.
It emits source-level aliases without the leading underscore together with .type and .dim directives for supported scalar and array types.
Tested with PIC18F452 using current gputils:

• initialized and uninitialized scalar variables
• initialized and uninitialized arrays
• multidimensional array AUX records
• fixed-address scalar UDATA
• gpasm/gpvo COFF inspection
• variable type information verified in an external debugger
  With --debug-xtra disabled, the existing assembler output remains unchanged.
  The patch was verified to apply cleanly to SVN r16960.