Add type annotation for step_into opts; correct docs

Author: mfussenegger

doc/dap.txt

@@ -791,12 +791,12 @@ step_into([{opts}])                                            *dap.step_into()*
         If it cannot step into a function or method it behaves like
         |dap.step_over()|.
 
-        If the debug adapter has the `supportsStepInTargetsRequest` and  
-        {ask_for_targets} is true, the user can choose into which function they
-        want to step into if there are multiple.
+        If the debug adapter has the `supportsStepInTargetsRequest` capability and
+        {askForTargets} is true, the user can choose into which function they
+        want to step into if there are multiple choices.
 
         Some debug adapters allow a more fine-grained control over the
-        behavior of this command using the {opts} parameter:
+        behavior of this command using the `steppingGranularity` {opts} parameter:
 
         steppingGranularity:
           Can be 'statement' | 'line' | 'instruction'

lua/dap.lua

@@ -563,6 +563,7 @@ function M.restart_frame()
 end
 
 
+---@param opts? {askForTargets?: boolean, steppingGranularity?: dap.SteppingGranularity}
 function M.step_into(opts)
   session = first_stopped_session()
   if not session then

lua/dap/protocol.lua

@@ -246,3 +246,6 @@
 ---@class dap.StartDebuggingRequestArguments
 ---@field configuration table<string, any>
 ---@field request 'launch'|'attach'
+
+
+---@alias dap.SteppingGranularity 'statement'|'line'|'instruction'