More assorted ICU4C DecimalFormat optimizations.

More assorted ICU4C DecimalFormat optimizations.

[sffc, 2018-04-21 08:02:45]

https://codereview.appspot.com/343000043/diff/1/i18n/decimfmt.cpp
File i18n/decimfmt.cpp (left):

https://codereview.appspot.com/343000043/diff/1/i18n/decimfmt.cpp#oldcode1
i18n/decimfmt.cpp:1: // © 2018 and later: Unicode, Inc. and others.
I guess I should also port this value-checking logic to ICU4J?

https://codereview.appspot.com/343000043/diff/1/i18n/decimfmt.cpp#oldcode102
i18n/decimfmt.cpp:102: void
DecimalFormat::setParseAllInput(UNumberFormatAttributeValue value) {
A good thing to do in review is make sure that I am doing all the checks
correctly (i.e., no typos like checking the wrong property in the method).  I
think I got them all right but it's easy to miss one.

https://codereview.appspot.com/343000043/diff/1/i18n/decimfmt.cpp#oldcode1256
i18n/decimfmt.cpp:1256: if (++group == 3 && fFastData.cpGroupingSeparator != 0)
{
Having this at the end of the loop was causing strings like ",999" to be
printed.  Moving it to the beginning is correct.

https://codereview.appspot.com/343000043/diff/1/i18n/measunit.cpp
File i18n/measunit.cpp (left):

https://codereview.appspot.com/343000043/diff/1/i18n/measunit.cpp#oldcode1121
i18n/measunit.cpp:1121: initNoUnit("base");
The default constructor of MeasureUnit is called thousands and thousands of
times throughout the test suite, since every NumberFormatter has one as a member
field by value.  Squeezing every little bit of performance out of it is good. 
This change replaces a string comparison and binary search with direct setters.

https://codereview.appspot.com/343000043/diff/1/i18n/measunit.cpp
File i18n/measunit.cpp (right):

https://codereview.appspot.com/343000043/diff/1/i18n/measunit.cpp#newcode562
i18n/measunit.cpp:562: static const int32_t kBaseSubTypeIdx = 0;
I added this to the auto-generate function, which isn't in this review.

https://codereview.appspot.com/343000043/diff/1/i18n/number_decimfmtprops.cpp
File i18n/number_decimfmtprops.cpp (left):

https://codereview.appspot.com/343000043/diff/1/i18n/number_decimfmtprops.cpp...
i18n/number_decimfmtprops.cpp:94: eq = eq && minimumFractionDigits ==
other.minimumFractionDigits;
minFrac == 0 is sufficient for fastpath.  Moving it out of the mandatory
equivalents and into the optional equivalents with additional logic to handle
that case in decimfmt.cpp