[lldb] Implement a statusline in LLDB (#121860)

Add a statusline to command-line LLDB to display information about the
current state of the debugger. The statusline is a dedicated area
displayed at the bottom of the screen. The information displayed is
configurable through a setting consisting of LLDB’s format strings.

Enablement
----------

The statusline is enabled by default, but can be disabled with the
following setting:

```
(lldb) settings set show-statusline false
```

Configuration
-------------

The statusline is configurable through the `statusline-format` setting.
The default configuration shows the target name, the current file, the
stop reason and any ongoing progress events.

```
(lldb) settings show statusline-format
statusline-format (format-string) = "${ansi.bg.blue}${ansi.fg.black}{${target.file.basename}}{ | ${line.file.basename}:${line.number}:${line.column}}{ | ${thread.stop-reason}}{ | {${progress.count} }${progress.message}}"
```

The statusline supersedes the current progress reporting implementation.
Consequently, the following settings no longer have any effect (but
continue to exist to not break anyone's `.lldbinit`):

```
show-progress             -- Whether to show progress or not if the debugger's output is an interactive color-enabled terminal.
show-progress-ansi-prefix -- When displaying progress in a color-enabled terminal, use the ANSI terminal code specified in this format immediately before the progress message.
show-progress-ansi-suffix -- When displaying progress in a color-enabled terminal, use the ANSI terminal code specified in this format immediately after the progress message.
```

Format Strings
--------------

LLDB's format strings are documented in the LLDB documentation and on
the website: https://lldb.llvm.org/use/formatting.html#format-strings.
The current implementation is relatively limited but various
improvements have been discussed in the RFC.

One such improvement is being to display a string when a format string
is empty. Right now, when launching LLDB without a target, the
statusline will be empty, which is expected, but looks rather odd.

RFC
---

The full RFC can be found on Discourse:
https://discourse.llvm.org/t/rfc-lldb-statusline/83948

1 files changed, 3 insertions, 0 deletions

diff --git a/lldb/packages/Python/lldbsuite/test/lldbtest.py b/lldb/packages/Python/lldbsuite/test/lldbtest.py
index f117aea..a055314 100644
--- a/lldb/packages/Python/lldbsuite/test/lldbtest.py
+++ b/lldb/packages/Python/lldbsuite/test/lldbtest.py
@@ -772,7 +772,10 @@ class Base(unittest.TestCase):
             'settings set symbols.clang-modules-cache-path "{}"'.format(
                 configuration.lldb_module_cache_dir
             ),
+            # Disable colors by default.
             "settings set use-color false",
+            # Disable the statusline by default.
+            "settings set show-statusline false",
         ]
 
         # Set any user-overridden settings.