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.

These are hardcoded strings that are already present in the data section
of the binary, no need to immediately place them in the ConstString
StringPools. Lots of code still calls `GetBroadcasterClass` and places
the return value into a ConstString. Changing that would be a good
follow-up.

Additionally, calls to these functions are still wrapped in ConstStrings
at the SBAPI layer. This is because we must guarantee the lifetime of
all strings handed out publicly.

A user found a crash when they would do code like:
```
(lldb) script
>>> target = lldb.SBTarget()
>>> lldb.debugger.SetSelectedTarget(target)
```

We were not checking if the target was valid in and it caused a crash..

This patch replaces uses of StringRef::{starts,ends}with with
StringRef::{starts,ends}_with for consistency with
std::{string,string_view}::{starts,ends}_with in C++20.

I'm planning to deprecate and eventually remove
StringRef::{starts,ends}with.

Also, make it possible for new Targets which haven't been added to
the TargetList yet to check for interruption, and add a few more
places in building modules where we can check for interruption.

Differential Revision: https://reviews.llvm.org/D154542

This patch add the ability for the user to set a label for a target.

This can be very useful when debugging targets with the same executables
in the same session.

Labels can be set either at the target creation in the command
interpreter or at any time using the SBAPI.

Target labels show up in the `target list` output, following the target
index, and they also allow the user to switch targets using them.

rdar://105016191

Differential Revision: https://reviews.llvm.org/D151859

Signed-off-by: Med Ismail Bennani <ismail@bennani.ma>

This reverts commit 2d53527e9c64c70c24e1abba74fa0a8c8b3392b1.