Reads the character code at the start of text.
public CharacterCode ReadCode(ReadOnlySpan<byte> text)
The rest of a string shown in a composite font.
false and the length of the codespace range that best matches its first bytes; never more bytes than
text has. An empty text gives a code of length 0.
ISO 32000-2 §9.7.6.2: one byte is matched against the one-byte codespace ranges, then two against the two-byte ranges, up to four. §9.7.6.3 for an invalid code: when no range admits its first byte, the shortest codes are used; otherwise the range matching the most leading bytes (the shortest of equals) gives the length. Allocates nothing.