`[]<list<int>>` actually produces `list<list<int>>`.

In Record only store the direct superclasses instead of all
superclasses. getSuperClasses recurses to find all superclasses when
necessary.

This gives a small reduction in memory usage. On lib/Target/X86/X86.td I
measured about 2.0% reduction in total bytes allocated (measured by
valgrind) and 1.3% reduction in peak memory usage (measured by
/usr/bin/time -v).

---------

Co-authored-by: Min-Yih Hsu <min@myhsu.dev>

The format is: `!instances<T>([regex])`.
    
This operator produces a list of records whose type is `T`. If
`regex` is provided, only records whose name matches the regular
expression `regex` will be included. The format of `regex` is ERE
(Extended POSIX Regular Expressions).

The grammar is `!match(str, regex)` and this operator produces 1
if the `str` matches the regular expression `regex`.

The format of `regex` is ERE (Extended POSIX Regular Expressions).

These were referring to nonexistent grammar tokens instead of `Value`.

Previously the grammar tokens SimpleValue2 through SimpleValue9 were
unreferenced. This ties them together so that the grammar makes more
sense.

Previously the Type production did not include "code", which was only
accepted in one place in the grammar:

   BodyItem: (`Type` | "code") `TokIdentifier` ["=" `Value`] ";"

However the parser implementation accepts "code" as a Type with only one
place where it is *not* allowed, corresponding to this production:

   SimpleValue9: `BangOperator` ["<" `Type` ">"] "(" `ValueListNE` ")"

This patch changes the production for Type to include "code", thereby
fixing most occurrences of Type in the grammar, and documents the
restriction for BangOperator Types in the text instead of codifying it
in the grammar.

SearchIndex doesn't support ReturnRange. It is only supported for
the primary key.

There are cases (like in an upcoming patch to MLIR's `Property` class)
where the ? value is a useful null value. However, existing predicates
make ti difficult to test if the value in a record one is operating is ?
or not.

This commit adds the !initialized predicate, which is 1 on concrete,
non-? values and 0 on ?.

---------

Co-authored-by: Akshat Oke <Akshat.Oke@amd.com>