feat: add hide / unhide preview (#1305)

* feat: add hide / unhide preview or results and prompt

* fix edit actions while only preview window is active

* add option to start telescope without previewer -> "disable_previewer_at_startup"

* remove hide / unhide prompt and resutls, improve hide / unhide preview

* fix tests - check if popup window should be created with borders - popup.create does not support setting borderhighlight and border=false

* allow toggle preview even if preview is set to false

* reuse recalculate_layout in hide / unhide preview

* add docs to toggle preview

* check if preview window is valid window

* remove unnecessary changes

* cleanup, remove unnecessary changes

* close all previewers, refactor toggle preview code

[docgen] Update doc/telescope.txt
skip-checks: true

doc/telescope.txt

@@ -395,6 +395,9 @@ telescope.setup({opts})                                    *telescope.setup()*
                               Default: true
           - msg_bg_fillchar:  Character to fill background of unpreviewable buffers with
                               Default: "╱"
+          - hide_on_startup:  Hide previewer when picker starts. Previewer can be toggled
+                              with actions.toggle_preview.
+                              Default: false
 
 
                                      *telescope.defaults.vimgrep_arguments*
@@ -1909,6 +1912,15 @@ actions.toggle_all({prompt_bufnr})                      *actions.toggle_all()*
         {prompt_bufnr} (number)  The prompt bufnr
 
 
+actions.toggle_preview({prompt_bufnr})              *actions.toggle_preview()*
+    Toggle preview window.
+    - Note: preview window can be toggled even if preview is set to false.
+
+
+    Parameters: ~
+        {prompt_bufnr} (number)  The prompt bufnr
+
+
 actions.git_create_branch({prompt_bufnr})        *actions.git_create_branch()*
     Create and checkout a new git branch if it doesn't already exist