Allow four more characters to start identifiers.

- Mathematical bold 0, 1 (U+1D7CE, U+1D7CF)
- Mathematical double-struck 0, 1 (U+1D7D8, U+1D7D9)

which are sometimes used to represent certain representations of additive
and multiplicative identities.

Closes #10762

src/flisp/julia_extensions.c

@@ -84,6 +84,9 @@ static int is_wc_cat_id_start(uint32_t wc, utf8proc_propval_t cat)
  (wc >= 0x2a09 && wc <= 0x2a16) || // ⨉, ⨊, ⨋, ⨌, ⨍, ⨎, ⨏, ⨐, ⨑, ⨒, ⨓, ⨔, ⨕, ⨖
  wc == 0x2a1b || wc == 0x2a1c)))) || // ⨛, ⨜
 
+ (wc == 0x1d7ce || wc <= 0x1d7cf ) || // Mathematical bold 0, 1
+ (wc == 0x1d7d8 || wc <= 0x1d7d9 ) || // Mathematical double-struck 0, 1
+
  (wc >= 0x1d6c1 && // variants of \nabla and \partial
  (wc == 0x1d6c1 || wc == 0x1d6db ||
  wc == 0x1d6fb || wc == 0x1d715 ||