fn:format-number: add parameter for explicit format; use DecimalFormatSymbols to predefine formats for languages

[GuntherRademacher]

These changes implement fn:format-number as specified in qt4cg/qtspecs#340:

• a fourth parameter format is added for supplying an explicit format,
• language identifiers of available locales are used to predefine a decimal format for a language. This is accomplished by getting the symbols from either java.text.DecimalFormatSymbols, or com.ibm.icu.text.DecimalFormatSymbols.

Also the remaining 7 test failures from format-number.xml are fixed. It took two individual changes to do this:

• grouping separators in the fractional part were ignored
• the analysis for regular grouping was incomplete, in that i allowed digits making up more than one group at the beginning of the picture.

[ChristianGruen]

Just merged (via a local branch).

The solution was fine! I’ve further unified the decimal-format handling by replacing the constant strings with the new DecimalFormatOptions class.