Add docs for most vim.lsp methods

Most of the lsp.log will be addressed in a separate PR.

runtime/lua/vim/lsp/log.lua

@@ -21,12 +21,14 @@ local log_date_format = "%FT%H:%M:%S%z"
 
 do
   local path_sep = vim.loop.os_uname().sysname == "Windows" and "\\" or "/"
+  --@private
   local function path_join(...)
     return table.concat(vim.tbl_flatten{...}, path_sep)
   end
   local logfilename = path_join(vim.fn.stdpath('data'), 'lsp.log')
 
-  --- Return the log filename.
+  --- Returns the log filename.
+  --@returns (string) log filename
   function log.get_filename()
     return logfilename
   end
@@ -74,6 +76,8 @@ end
 -- interfere with iterating the levels
 vim.tbl_add_reverse_lookup(log.levels)
 
+--- Sets the current log level.
+--@param level (string or number) One of `vim.lsp.log.levels`
 function log.set_level(level)
   if type(level) == 'string' then
     current_log_level = assert(log.levels[level:upper()], string.format("Invalid log level: %q", level))
@@ -84,8 +88,9 @@ function log.set_level(level)
   end
 end
 
--- Return whether the level is sufficient for logging.
--- @param level number log level
+--- Checks whether the level is sufficient for logging.
+--@param level number log level
+--@returns (bool) true if would log, false if not
 function log.should_log(level)
   return level >= current_log_level
 end