Extended RTTI

Extended RTTI must be extended to enable Delphi compatible behaviour.

• Support for $RTTI directive
    - includes both EXPLICIT and INHERIT options
    - includes TVisibilityClasses set type
    - includes DefaultFieldRttiVisibility, DefaultMethodRttiVisibility and DefaultPropertyRttiVisibility constants
    - by default values of the Default*RttiVisibility constants is Delphi compatible with the following restrictions:
      - the constants can be forced to '[]' by passing a define (e.g. RTL_NO_EX_RTTI) when building the RTL
      - on resource restricted systems the constants have by default the value '[]'
        - this includes at least the CPUs i8086 and AVR
        - and at least the targets GBA, NDS, Wii, Amiga68k, GO32V2
        - this can be avoided by compiling the RTL with a define (e.g. RTL_FORCE_EX_RTTI)

• Generating the RTTI metadata for fields, methods and properties
    - this includes classes, records and helper types
    - the record format should in principle be usable for the object type as well (which does not have RTTI enabled currently)
    - interface types should obey the $RTTI switch as well in addition to $M
        Note: Raw interfaces currently don't have additional RTTI (properties, methods enabled), but the data should in principle work for those as well
    - the format of the new RTTI metadata should be Delphi compatible where it doesn't make sense to implement something faster (especially related to enumeration of the data) - e.g. identifier names can be
  implemented using references to shared string data as is done in the RTTI for interface methods
    - the format of the new RTTI metadata should be as source compatible as reasonably possible to old, existing FPC code
    - check how extended RTTI is handled for generic methods in Delphi (both the generic and the specialization)
    - new metadata should contain pointers to a TAttributeTable
    - the compiler should fill this already (all defs and syms already have a corresponding field)
    - having the compiler bind attributes to fields, methods, properties is not yet necessary (though if desired it can be implemented already as well)

• Support for accessing the extended RTTI in the TypInfo unit

• Support for accessing the extended RTTI in the RTTI unit (preferrably using functionality of the TypInfo unit to avoid code duplication)

• Explicitely not part of this assignment:

  • enumerating types in a unit/the whole program
  • $WEAKLINKRTTI (which relies on the above point)

• Tests for both the lowlevel functionality as well as the TypInfo/RTTI units, that should pass at least on the following platforms:
    - any i386 or x86_64 target
    - any arm target (32-bit) (due to alignment hassle)
    - a Big Endian target
    - i8086-msdos with both near pointers and far pointers
    Note: it's enough for the tests to pass in a VM (e.g. QEMU's user mode VM for ARM and the Big Endian target and DOSBox for MSDOS)

• Further fixes/functionality for the RTTI unit that are independent of the Extended RTTI feature
  (e.g. fixes for TValue type) should be reported/provided independently and ASAP as that unit is otherwise actively used and developed on