[lldb] Fix the DWARF index cache when index is partial. (#118390)

The ManualDWARFIndex class can create a index cache if the LLDB index
cache is enabled. This used to save the index to the same fil

[lldb] Fix the DWARF index cache when index is partial. (#118390)

The ManualDWARFIndex class can create a index cache if the LLDB index
cache is enabled. This used to save the index to the same file,
regardless of wether the cache was a full index (no .debug_names) or a
partial index (have .debug_names, but not all .o files were had
.debug_names). So we could end up saving an index cache that was
partial, and then later load that partial index as if it were a full
index if the user set the 'settings set
plugin.symbol-file.dwarf.ignore-file-indexes true'. This would cause us
to ignore the .debug_names section, and if the index cache was enabled,
we could end up loading the partial index as if it were a full DWARF
index.

This patch detects when the ManualDWARFIndex is being used with
.debug_names, and saves out a cache file with a suffix of "-full" or
"-partial" to avoid this issue.

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