[lldb][windows] Allow exporting plugin symbols in LLDB_EXPORT_ALL_SYMBOLS (#71087)

Plugins aren't exported by default in the msvc path because we
explicitly limit the symbols exported to prevent hitting the symbol export limit.
Some plugins, however, can still be useful for downstream projects to
build on, e.g. the Mojo language uses parts of the dwarf plugin to
implement dwarf handling within its debugger plugin.

This PR adds a cmake variable in the MSVC path,
LLDB_EXPORT_ALL_SYMBOLS_PLUGINS, that allows for providing the set
of plugins to export symbols from.