getFontFaceNumber returns the index of the font in the collection,
font formats without indexes are now "0" rather than -1. All
existing code already converted < 0 to 0 anyway, so simplifys a
little.

Cell input in testDataPilotLabels() like 1.2.3 was prefixed with single
quote / apostrophe to not form a date input but string instead. With the
new date acceptance, in en-US locale 1.2.3 isn't a date anymore and the
quote becomes part of the cell content, so the test checking for 1.2.3
failed because the result was '1.2.3

Get rid of the lax "any 1-2 possible date separators used with 2-3 numbers
forms a date" date recognition. Use locale data's DateAcceptancePattern
elements to match against, or ISO 8601 yyyy-mm-dd, or an already applied date
format.

Special special.. upper and lower case letter GHE and space and non-breaking
space.

though I strongly doubt the entire US-centric approach ...

- Removed separators '-', '.' and '/' working in all combinations in all
  locales forcing a date even for 23/12.99 (if locale has DMY order)
* Only the locale's date separator is accepted, plus '-' if the input may
  represent an ISO 8601 date yyyy-mm-dd, check is lax though on minimum
  digits, y-m-d is also accepted.
* Additionally, accept yy-month-dd or dd-month-yy with month name. Year must
  be <1 or >31, 2-digit year magic for values 0,32..99 is applied, or has to
  be prefixed with leading zero.

+ Years < 100 without being hit by the 2 digits year magic can be entered by
  preceding them with a leading 0 if at least 3 digits are present, e.g.
  099-1-1 is year 99, not 1999.
+ Years < 100 in an yyyy format are always displayed as 0099.