[lldb] Use the terminal height for paging editline completions (#119914)

Currently, we arbitrarily paginate editline completions to 40 elements.
On large terminals, that leaves some real-estate unus

[lldb] Use the terminal height for paging editline completions (#119914)

Currently, we arbitrarily paginate editline completions to 40 elements.
On large terminals, that leaves some real-estate unused. On small
terminals, it's pretty annoying to not see the first completions. We can
address both issues by using the terminal height for pagination.

This builds on the improvements of #116456.

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[lldb] Improve editline completion formatting (#116456)

This patch improves the formatting of editline completions. The current
implementation is naive and doesn't account for the terminal width.

[lldb] Improve editline completion formatting (#116456)

This patch improves the formatting of editline completions. The current
implementation is naive and doesn't account for the terminal width.

Concretely, the old implementation suffered from the following issues:

- We would unconditionally pad to the longest completion. If that
completion exceeds the width of the terminal, that would result in a lot
of superfluous white space and line wrapping.
- When printing the description, we wouldn't account for the presence of
newlines, and they would continue without leading padding.

The new code accounts for both. If the completion exceeds the available
terminal width, we show what fits on the current lined followed by
ellipsis. We also no longer pad beyond the length of the current line.
Finally, we print the description line by line, with the proper leading
padding. If a line of the description exceeds the available terminal
width, we print ellipsis and won't print the next line.

Before:

```
Available completions:
_regexp-attach -- Attach to process by ID or name.
_regexp-break -- Set a breakpoint using one of several shorthand
formats.
_regexp-bt -- Show backtrace of the current thread's call sta
ck. Any numeric argument displays at most that many frames. The argument 'al
l' displays all threads. Use 'settings set frame-format' to customize the pr
inting of individual frames and 'settings set thread-format' to customize th
e thread header. Frame recognizers may filter thelist. Use 'thread backtrace
-u (--unfiltered)' to see them all.
_regexp-display -- Evaluate an expression at every stop (see 'help
target stop-hook'.)

```

After:
```
Available completions:
_regexp-attach -- Attach to process by ID or name.
_regexp-break -- Set a breakpoint using one of several shorth...
_regexp-bt -- Show backtrace of the current thread's call ...
_regexp-display -- Evaluate an expression at every stop (see 'h...
```

rdar://135818198

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