Completes the ToJSON function for `OptionValue` types and make the interface function pure virtual

---------

Co-authored-by: Jonas Devlieghere <jonas@devlieghere.com>

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 patch adds new SBDebugger::GetSetting() API which
enables client to access settings as SBStructedData.

Implementation wise, a new ToJSON() virtual function is added to OptionValue
class so that each concrete child class can override and provides its
own JSON representation. This patch aims to define the APIs and implement
a common set of OptionValue child classes, leaving the remaining for
future patches.

This patch is used later by auto deduce source map from source line breakpoint
feature for testing generated source map entries.

Differential Revision: https://reviews.llvm.org/D133038

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D130403

The amount of roundtrips between StringRefs, ConstStrings and std::strings is
getting a bit out of hand, this patch avoid the unnecessary roundtrips.

Reviewed By: wallace, aprantl

Differential Revision: https://reviews.llvm.org/D112863

.. and reduce the scope of others. They don't follow llvm coding
standards (which say they should be used only when the same effect
cannot be achieved with the static keyword), and they set a bad example.

Replace misc. StringConvert uses with llvm::to_integer()
and llvm::to_float(), except for cases where further refactoring is
planned.  The purpose of this change is to eliminate the StringConvert
API that is duplicate to LLVM, and less correct in behavior at the same
time.

Differential Revision: https://reviews.llvm.org/D110447

Some implementations of the DeepCopy function called the copy constructor that copied m_parent member instead of setting a new parent. Others just leaved the base class's members (m_parent, m_callback, m_was_set) empty.
One more problem is that not all classes override this function, e.g. OptionValueArgs::DeepCopy produces OptionValueArray instance, and Target[Process/Thread]ValueProperty::DeepCopy produces OptionValueProperty. This makes downcasting via static_cast invalid.

The patch implements idiom "virtual constructor" to fix these issues.
Add a test that checks DeepCopy for correct copying/setting all data members of the base class.

Differential Revision: https://reviews.llvm.org/D96952

Summary:
In this diff of mine D77186 I introduce a bug in the replace operation, where I was failing fast by mistake.
Besides, a similar problem existed in the insert-after operation, where it was failing fast.

Finally, the remove operation was wrong, as it was not using the indices provided by the users.

I fixed those issues and added some tests account for cases with multiple elements in these requests.

Reviewers: labath, clayborg

Reviewed By: labath

Subscribers: mgrang, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D77324