Rename isBmpLast, used for Unicode data

[slevithan]

In the Unicode data generators (under tools/) and Unicode addons, rename isBmpLast as the more descriptive hasOrphanHighSurrogatesAndAstral. It's only used for category C and property Any, so the long name doesn't matter.

• Or just hasOrphanHighSurrogates and let Unicode Base know to also check whether there is astral data before flipping the order of bmp and astral data.
• Or just hasOrphanSurrogates and let Unicode Base know to also check whether there is astral data before flipping the order. This would mean attaching this prop in more cases where it isn’t currently useful (either because there’s no astral data or there are only low surrogates), but that’s probably not so bad.

[slevithan]

I don't think this should be treated as a breaking change, since isBmpLast is unlikely to be used by any existing addons outside of the official XRegExp Unicode addons (which themselves barely use it).