Fit symbol_redirect snugly in two bits

Fit symbol_redirect snugly in two bits

This allows the C compiler to do away with all default clauses when
switching on the `redirect` field.

* src/lisp.h (enum symbol_redirect): Use values in the 0..3 range,
which also matches the old comment in struct Lisp_Symbol.
(enum symbol_interned, enum symbol_redirect)
(enum symbol_trapped_write): Comment members.  Remove explicit values.
(struct Lisp_Symbol): Shrink the `redirect` member to 2 bits.
Use the correct type for the `interned` field.
Move value comments to their types.
* src/pdumper.c (dump_symbol): Update hashes.