RegExp: fix match count computation

* There actually is a way to count the matches, so use it instead of
attempting to guess
* In some cases (when using optional groups (xxx)?, for example), there
may be a non-matching group (with offsets set to -1) and matching groups
after it, so the binary search wasn't quite working
* Instead, we always return the number of capturing groups in the in
the given expression, which is the maximal number of matches. Some (or
all) of these may not have any content. We do return 0 matches on any
error, including when the regular expression didn't match anything.

Add ability to specify case insensitive matching.

Import RegExp classes from Ham.

Minor adjustments made by myself to fit into Haiku better.

RegExp: fix match count computation

* There actually is a way to count the matches, so use it instead of
attempting to guess
* In some cases (when using optional groups (xxx)?, for example), there
may be a non-matching group (with offsets set to -1) and matching groups
after it, so the binary search wasn't quite working
* Instead, we always return the number of capturing groups in the in
the given expression, which is the maximal number of matches. Some (or
all) of these may not have any content. We do return 0 matches on any
error, including when the regular expression didn't match anything.

Add ability to specify case insensitive matching.

Import RegExp classes from Ham.

Minor adjustments made by myself to fit into Haiku better.