support Unicode 15.1 via utf8proc 2.9.0 (#51799)

Similar to #47392, support [Unicode
15.1](https://www.unicode.org/versions/Unicode15.1.0/) by bumping
utf8proc to 2.9.0 (JuliaStrings/utf8proc#253).

This allows us to use [118 exciting new emoji
characters](https://blog.emojipedia.org/whats-new-in-unicode-15-1-and-emoji-15-1/)
as identifiers, including "edible mushroom" `"\U1f344\u200d\U1f7eb"`
(but still no superscript "q").

Interestingly, they also updated the [Unicode recommendations on
programming-language identifiers
(UAX#31)](https://www.unicode.org/reports/tr31/tr31-39.html#Mathematical_Compatibility_Notation_Profile)
to finally "bless" identifiers beginning with `∂` and `∇` and/or ending
with numeric sub/superscripts. They still don't recommend nearly the
range of identifiers accepted by Julia, however.

NEWS.md

@@ -8,6 +8,7 @@ New language features
   difference between `public` and `export` is that `public` names do not become
   available when `using` a package/module. ([#50105])
 * `ScopedValue` implement dynamic scope with inheritance across tasks ([#50958]).
+* Support for Unicode 15.1 ([#51799]).
 * A new `AbstractString` type, `AnnotatedString`, is introduced that allows for
   regional annotations to be attached to an underlying string. This type is
   particularly useful for holding styling information, and is used extensively

deps/checksums/utf8proc

@@ -1,2 +1,2 @@
-utf8proc-1cb28a66ca79a0845e99433fd1056257456cef8b.tar.gz/md5/aff37aadd1b02cad3259683e8a5f4543
-utf8proc-1cb28a66ca79a0845e99433fd1056257456cef8b.tar.gz/sha512/3ee433e5577e01f334aa4224275dfb7ee6ae7c785013df3eee6fc0488218d3bc895649811589edf57461c6520ad70437fbf6a376959a6a6f70bd920eb01c5001
+utf8proc-34db3f7954e9298e89f42641ac78e0450f80a70d.tar.gz/md5/e70e4fd2c914b4d4c0e3f0e2ca6c96d4
+utf8proc-34db3f7954e9298e89f42641ac78e0450f80a70d.tar.gz/sha512/0037f144e1150abd1b330d8a0c3a46c8352903acc9f4c8aad6bddd1370b19cc34551f8def58752cdff4eaace3efe54180bc11439a0e35c5ccad2fec4678c017e

deps/utf8proc.version

@@ -1,2 +1,2 @@
-UTF8PROC_BRANCH=v2.8.0
-UTF8PROC_SHA1=1cb28a66ca79a0845e99433fd1056257456cef8b
+UTF8PROC_BRANCH=v2.9.0
+UTF8PROC_SHA1=34db3f7954e9298e89f42641ac78e0450f80a70d