NFC patch which moves `DiagnosticsRendering` from `Utility` to `Host`.

This refactoring is needed for
https://github.com/llvm/llvm-project/pull/168603. It adds a method to
check whether the current terminal supports Unicode or not. This will be
OS dependent and a better fit for `Host`. Since `Utility` cannot depend
on `Host`, `DiagnosticsRendering` must live in `Host` instead.

There's no reason these methods cannot be `const`. Currently this
prevents us from passing around a const ref. This patch is in
preparation for #125006.

Building on top of previous work that exposed expression diagnostics via
SBCommandReturnObject, this patch generalizes the support to expose any
SBError as machine-readable structured data. One use-case of this is to
allow IDEs to better visualize expression diagnostics.

rdar://139997604

We have helpers to emit warnings and errors. Do the same thing for notes
to they stand out more.

This allows IDEs to render LLDB expression diagnostics to their liking
without relying on characterprecise ASCII art from LLDB. It is exposed
as a versioned SBStructuredData object, since it is expected that this
may need to be tweaked based on actual usage.

In a later commit, I want to add a method to access diagnostics as
actual structured data, which will make these function names rather
confusing.

and implement them for dwim-print (a.k.a. `p`) as an example.

The next step will be to expose them as structured data in
SBCommandReturnObject.

This is a cleanup that moves the API towards value semantics.

Currently the expression parser prints a mostly useless generic error before printing the compiler error:

  (lldb) p 1+x)
  error: expression failed to parse:
  error: <user expression 18>:1:3: use of undeclared identifier 'x'
  1+x)
     ^

This is distracting and as far as I can tell only exists to work
around the fact that the first "error: " is unconditionally injected
by CommandReturnObject. The solution is not very elegant, but the
result looks much better.

(Partially addresses rdar://110492710)

Differential Revision: https://reviews.llvm.org/D152590

Show the user the DBGError (if available) when dsymForUUID fails.

rdar://90949180

Differential revision: https://reviews.llvm.org/D123743