This update all of our Unicode tables to Unicode 15.1. This is a minor
version so only a relatively small numbers of characters are added,
mainly ideographs

https://www.unicode.org/versions/Unicode15.1.0/#Appendices_nb

startswith/endswith wrap starts_with/ends_with and will eventually go away (to more closely match string_view)

In a Unicode name was stored in a way that caused
a medial hyphen to be at the end of a a chunk, it would not
be properly ignored by the loose matching algorithm.

For example if `LEFT-TO-RIGHT OVERRIDE` was stored as
`LEFT-` [...], the `-` would not be ignored.

The generators now ensures nodes are not cut accross
medial hyphen boundaries.

Fixes #64161

Differential Revision: https://reviews.llvm.org/D156518

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716

This patch mechanically replaces None with std::nullopt where the
compiler would warn if None were deprecated.  The intent is to reduce
the amount of manual work required in migrating from Optional to
std::optional.

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716

Unicode 15.0 adds 4,489 characters, for a total of 149,186 characters.
These additions include 2 new scripts along with 20 new emoji characters,
and 4,193 CJK ideographs.

This changes modify most existing tables including
 - XID_Start/XID_Continue in Clang
 - The character name database (used by \N{} in Clang)
 - The list of formattable/printable codepoints
 - The case folding algorithm (which we had not updated since Unicode 9)
 - The list of nonspacing/enclosing marks used by the column width
   computation algorithm. The rest of the column width algorithm
   is not updated.

Reviewed By: tahonermann

Differential Revision: https://reviews.llvm.org/D133807