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.

`thread step-in` (and other step commands) take a `<thread-index>`, not a `<thread-id>`.

We noticed that `apropos backtrace` did not return the `bt` alias. This change adds the 
word "backtrace" to the help for `bt`. It also updates `thread backtrace` to keep the 
language used roughly in sync.

Note that StringRef::equals has been deprecated in favor of
operator==(StringRef, StringRef).

This is another step towards supporting DWARF5 checksums and inline
source code in LLDB. This is a reland of #85468 but without the
functional change of storing the support file from the line table (yet).

Reverts llvm/llvm-project#85468 because @slackito reports this broke
stepping in one of their tests [1] and this patch was meant to be NFC.

[1]
https://github.com/llvm/llvm-project/commit/d5a277d309e92b1d3e493da6036cffdf815105b1#commitcomment-139991120

This is another step towards supporting DWARF5 checksums and inline
source code in LLDB.

The help output for `thread backtrace` specifies that you can pass -1 to
`--count` to display all the frames.

```
-c <count> ( --count <count> )
            How many frames to display (-1 for all)
```

However, that doesn't work:

```
(lldb) thread backtrace --count -1
error: invalid integer value for option 'c'
```

The problem is that we store the option value as an unsigned and the
code to parse the string correctly rejects it. There's two ways to fix
this:

1. Make `m_count` a signed value so that it accepts negative values and
appease the parser. The function that prints the frames takes an
unsigned so a negative value will just become a really large positive
value, which is what the current implementation relies on.
2. Keep `m_count` unsigned and instead use 0 the magic value to show all
frames. I don't really see a point in not showing any frames at all,
plus that's already broken (`error: error displaying backtrace for
thread: "0x0001"`).

This patch implements (2) and at the same time improve the error
reporting so that we print the invalid value when we cannot parse it.

rdar://123881767

Partly, there's just a lot of unnecessary boiler plate. It's also
possible to define combinations of arguments that make no sense (e.g.
eArgRepeatPlus followed by eArgRepeatPlain...) but these are never
checked since we just push_back directly into the argument definitions.

This commit is step 1 of this cleanup - do the obvious stuff. In it, all
the simple homogenous argument lists and the breakpoint/watchpoint
ID/Range types, are set with common functions. This is an NFC change, it
just centralizes boiler plate. There's no checking yet because you can't
get a single argument wrong.

The end goal is that all argument definition goes through functions and
m_arguments is hidden so that you can't define inconsistent argument
sets.