feat: Action improvements (#472)

* feat: replace_map

* feat: Add action_set and action_state

* fix: Move all actions.get_ to action_state.get_

* fix: replace all internal references of _goto_file_selection_edit

* feat: add some docs

* fix: lint

* feat: actions.select

* remove mentions and usage of goto_file_selection APIs

* feat: special case attach_mappings to be overridable and defaultable

* Having goto_file_selection mappings will cause a error

as well as replacing deprecated goto_file_selection methodes

For config and replacing use this instead:
- actions.select_default
- actions.select_horizonal
- actions.select_vertical
- actions.select_tab

Only replacing:
- actions.set.edit -- for replacing all select functions

* adds actions.state.select_key_to_edit_key

Co-authored-by: Simon Hauser <Simon-Hauser@outlook.de>

developers.md

@@ -0,0 +1,56 @@
+
+
+## Overriding actions/action_set
+
+How to override what different functions / keys do.
+
+TODO: Talk about what actions vs actions sets are
+
+### Relevant Files
+
+- `lua/telescope/actions/init.lua`
+    - The most "user-facing" of the files, which has the actions we provide builtin
+- `lua/telescope/actions/set.lua`
+    - The second most "user-facing" of the files. This provides actions that are consumed by several builtin actions, which allows for only overriding ONE item, instead of copying the same configuration / function several times.
+- `lua/telescope/actions/state.lua`
+    - Provides APIs for interacting with the state of telescope while in actions.
+    - These are most useful for writing your own actions and interacting with telescope at that time
+- `lua/telescope/actions/mt.lua`
+    - You probably don't need to look at this, but it defines the behavior of actions.
+
+### `:replace(function)`
+
+Directly override an action with a new function
+
+```lua
+local actions = require('telescope.actions')
+actions.select_default:replace(git_checkout_function)
+```
+
+### `:replace_if(conditional, function)`
+
+Override an action only when `conditional` returns true.
+
+```lua
+local action_set = require('telescope.actions.set')
+action_set.select:replace_if(
+  function()
+    return action_state.get_selected_entry().path:sub(-1) == os_sep
+  end, function(_, type)
+    -- type is { "default", "horizontal", "vertical", "tab" }
+    local path = actions.get_selected_entry().path
+    actions.refresh(prompt_bufnr, gen_new_finder(vim.fn.expand(path:sub(1, -2))), { reset_prompt = true })
+  end
+)
+```
+
+### `:replace_map(configuration)`
+
+```lua
+local action_set = require('telescope.actions.set')
+-- Use functions as keys to map to which function to execute when called.
+action_set.select:replace_map {
+  [function(e) return e > 0 end] = function(e) return (e / 10) end,
+  [function(e) return e == 0 end] = function(e) return (e + 10) end,
+}
+```