Use dfa to speed up translating UTF-8 into code point

Use dfa to speed up translating UTF-8 into code point

This dfa is available from the internet has the reputation of being the
fastest general translator.  This commit changes to use it at the
beginning of our translator, modifying it slightly to accept surrogates
and all 4-byte Perl-extended.  If necessary, it drops down into our
translator to handle errors and warnings and Perl extended.

It shows some improvement over our base translation:

Key:
    Ir   Instruction read
    Dr   Data read
    Dw   Data write
    COND conditional branches
    IND  indirect branches
    _m   branch predict miss
    -    indeterminate percentage (e.g. 1/0)

The numbers represent raw counts per loop iteration.

unicode::utf8n_to_uvchr_0x007f
ord(X)

       blead   dfa Ratio %
       ----- ----- -------
    Ir 359.0 359.0   100.0
    Dr 111.0 111.0   100.0
    Dw  64.0  64.0   100.0
  COND  42.0  42.0   100.0
   IND   5.0   5.0   100.0

COND_m   2.0   0.0     Inf
 IND_m   5.0   5.0   100.0

unicode::utf8n_to_uvchr_0x07ff
ord(X)

       blead   dfa Ratio %
       ----- ----- -------
    Ir 478.0 467.0   102.4
    Dr 132.0 133.0    99.2
    Dw  79.0  78.0   101.3
  COND  63.0  57.0   110.5
   IND   5.0   5.0   100.0

COND_m   1.0   0.0     Inf
 IND_m   5.0   5.0   100.0

unicode::utf8n_to_uvchr_0xfffd
ord(X)

       blead   dfa Ratio %
       ----- ----- -------
    Ir 494.0 486.0   101.6
    Dr 134.0 136.0    98.5
    Dw  79.0  78.0   101.3
  COND  67.0  61.0   109.8
   IND   5.0   5.0   100.0

COND_m   2.0   0.0     Inf
 IND_m   5.0   5.0   100.0

unicode::utf8n_to_uvchr_0x1fffd
ord(X)

       blead   dfa Ratio %
       ----- ----- -------
    Ir 508.0 505.0   100.6
    Dr 135.0 139.0    97.1
    Dw  79.0  78.0   101.3
  COND  70.0  65.0   107.7
   IND   5.0   5.0   100.0

COND_m   2.0   1.0   200.0
 IND_m   5.0   5.0   100.0

unicode::utf8n_to_uvchr_0x10fffd
ord(X)

       blead   dfa Ratio %
       ----- ----- -------
    Ir 508.0 505.0   100.6
    Dr 135.0 139.0    97.1
    Dw  79.0  78.0   101.3
  COND  70.0  65.0   107.7
   IND   5.0   5.0   100.0

COND_m   2.0   1.0   200.0
 IND_m   5.0   5.0   100.0

Each code point represents an extra byte required in its UTF-8
representation from the previous one.