feat: Consistent and sensible layout_config (#922)

* feat: Consistent and sensible layout_config

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

* [WIP]: Thu 17 Jun 2021 03:36:44 PM EDT

* [WIP]: Thu 17 Jun 2021 03:38:11 PM EDT

* layout_default -> layout_defaults

* remove options from bug repot

* Conni2461 suggestions: part 1

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

* Conni2461 suggestions: part 2

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

* Linting

* Improve deprecation checks

- Move `layout_defaults` handling to `deprecated.lua`
- Check for "layout keys" outside of `layout_config` on `setup`

* fixup: Just add a few more words

Co-authored-by: Luke Kershaw <35707277+l-kershaw@users.noreply.github.com>
Co-authored-by: Github Actions <actions@github>

doc/telescope_changelog.txt

@@ -0,0 +1,51 @@
+================================================================================
+                                                         *telescope.changelog*
+
+# Changelog
+
+                                                     *telescope.changelog-922*
+
+Date: May 17, 2021
+PR: https://github.com/nvim-telescope/telescope.nvim/pull/922
+
+This is one of our largest breaking changes thus far, so I (TJ) am adding some
+information here so that you can more easily update (without having to track
+down the commit, etc.).
+
+The goal of these breaking changes is to greatly simplify the way
+configuration for layouts happen. This should make it much easier to configure
+each picker, layout_strategy, and more. Please report any bugs or behavior
+that is broken / confusing upstream and we can try and make the configuration
+better.
+
+|telescope.setup()| has changed `layout_defaults` -> `layout_config`.
+    This makes it so that the setup and the pickers share the same key,
+    otherwise it is too confusing which key is for which.
+
+
+`picker:find()` now has different values available for configuring the UI.
+    All configuration for the layout must be passed in the key:
+        `layout_config`.
+
+    Previously, these keys were passed via `picker:find(opts)`, but should be
+    passed via `opts.layout_config` now.
+        - {height}
+        - {width}
+        - {prompt_position}
+        - {preview_cutoff}
+
+    These keys are removed:
+        - {results_height}: This key is no longer valid. Instead, use `height`
+          and the corresponding `preview_*` options for the layout strategy to
+          get the correct results height. This simplifies the configuration
+          for many of the existing strategies.
+
+        - {results_width}: This key actually never did anything. It was
+          leftover from some hacking that I had attempted before. Instead you
+          should be using something like the `preview_width` configuration
+          option for |layout_strategies.horizontal()|
+
+    You should get error messages when you try and use any of the above keys now.
+
+
+ vim:tw=78:ts=8:ft=help:norl: