ValueObject is part of lldbCore for historical reasons, but conceptually
it deserves to be its own library. This does introduce a (link-time) circular
dependency between lldbCore and lldbValueObject, which is unfortunate
but probably unavoidable because so many things in LLDB rely on
ValueObject. We already have cycles and these libraries are never built
as dylibs so while this doesn't improve the situation, it also doesn't
make things worse.

The header includes were updated with the following command:

```
find . -type f -exec sed -i.bak "s%include \"lldb/Core/ValueObject%include \"lldb/ValueObject/ValueObject%" '{}' \;
```

We have got customer reporting "v &obj" and "p &obj" reporting different
results.
Turns out it only happens for obj that is itself a reference type which
"v &obj" reports the address of the reference itself instead of the
target object the reference points to. This diverged from C++ semantics.

This PR fixes this issue by returning the address of the dereferenced
object if it is reference type.

A new test is added which fails before.

Co-authored-by: jeffreytan81 <jeffreytan@fb.com>

This PR adds a statistics provider cache, which allows an individual
target to keep a rolling tally of it's total time and number of
invocations for a given summary provider. This information is then
available in statistics dump to help slow summary providers, and gleam
more into insight into LLDB's time use.

This patch removes all of the Set.* methods from Status.

This cleanup is part of a series of patches that make it harder use the
anti-pattern of keeping a long-lives Status object around and updating
it while dropping any errors it contains on the floor.

This patch is largely NFC, the more interesting next steps this enables
is to:
1. remove Status.Clear()
2. assert that Status::operator=() never overwrites an error
3. remove Status::operator=()

Note that step (2) will bring 90% of the benefits for users, and step
(3) will dramatically clean up the error handling code in various
places. In the end my goal is to convert all APIs that are of the form

`    ResultTy DoFoo(Status& error)
`
to

`    llvm::Expected<ResultTy> DoFoo()
`
How to read this patch?

The interesting changes are in Status.h and Status.cpp, all other
changes are mostly

` perl -pi -e 's/\.SetErrorString/ = Status::FromErrorString/g' $(git
grep -l SetErrorString lldb/source)
`
plus the occasional manual cleanup.

This is de facto an NFC change for Objective-C but will benefit the
Swift language plugin.

This change by itself has no measurable effect on the LLDB
testsuite. I'm making it in preparation for threading through more
errors in the Swift language plugin.

Create additional helper functions for the ValueObject class, for:
  - returning the value as an APSInt or APFloat
  - additional type casting options
  - additional ways to create ValueObjects from various types of data
  - dereferencing a ValueObject

These helper functions are needed for implementing the Data Inspection
Language, described in
https://discourse.llvm.org/t/rfc-data-inspection-language/69893

The the function is doing two fairly different things, depending on how
it is called. While this allows for some code reuse, it also makes it
hard to override it correctly. Possibly for this reason
ValueObjectSynthetic overerides GetChildAtIndex instead, which forces it
to reimplement some of its functionality, most notably caching of
generated children.

Splitting this up makes it easier to move the caching to a common place
(and hopefully makes the code easier to follow in general).

UpdateFormatsIfNeeded has hardcoded the call to GetFormat with no
dynamic values. GetFormat will try to find the synthetic children of the
ValueObject, and passing the wrong one can fail, which can be bad for
performance but should not be user visible. Fix the performace bug by
passing the dynamic value type of the ValueObject.

rdar://122506593