feat: layout_strategies refactor (#1039)

* wip: 2021-07-22 15:00 BST

* wip: `horizontal` refactored

* wip: `center` refactored

* wip: `cursor` and `vertical` refactored

* wip: `current_buffer` refactor

- also changed `layout_config_defaults` as they gave errors when using `current_buffer`

* wip: `bottom_pane` refactor

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

* fix: put accidentally remove config option back

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

* wip: standardise `height` calculation for `center` and `bottom_pane`

* wip: improve comments

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

* stylua

- also fix a merge mistake

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

* fix: attempt to fix bad merge

* refactor: remove unused entry in `borderchars` table

- also fix some typos

* wip: tweak padding for `bottom_pane`

* wip: add `tabline` checks to `bottom_pane`

- also tweaked position so that `statusline` is not covered when borders are enabled

* stylua

* refactor: factor out size capping function

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

* fix: adjust tests that relied on height being number of results

* fix: forgot variable in calc_size_and_spacing

* fix: maybe this fixes these tests?

* test: try other plenary branch for ci

* test: switch back to main plenary branch for ci

* fix: actually define `max_results` in the test

* fix: final tweaks for edge cases

Co-authored-by: Github Actions <actions@github>

doc/telescope.txt

@@ -113,21 +113,30 @@ telescope.setup({opts})                                    *telescope.setup()*
         of 50% of the screen width.
 
         Default: {
+          bottom_pane = {
+            height = 25
+          },
           center = {
-            preview_cutoff = 40
+            height = 0.9,
+            preview_cutoff = 40,
+            width = 0.8
           },
           cursor = {
-            preview_cutoff = 40
+            height = 0.9,
+            preview_cutoff = 40,
+            width = 0.8
           },
-          height = 0.9,
           horizontal = {
+            height = 0.9,
             preview_cutoff = 120,
-            prompt_position = "bottom"
+            prompt_position = "bottom",
+            width = 0.8
           },
           vertical = {
-            preview_cutoff = 40
-          },
-          width = 0.8
+            height = 0.9,
+            preview_cutoff = 40,
+            width = 0.8
+          }
         }