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>

lua/tests/automated/pickers/find_files_spec.lua

@@ -38,9 +38,10 @@ describe("builtin.find_files", function()
           sorter = require('telescope.sorters').get_fzy_sorter(),
           layout_strategy = 'center',
           layout_config = {
-            height = max_results,
+            height = max_results + 1,
             width = 0.9,
           },
+          border = false,
         }, vim.fn.json_decode([==[%s]==])))
       ]],
         vim.fn.json_encode(configuration)
@@ -57,6 +58,8 @@ describe("builtin.find_files", function()
 
       tester.run_string(string.format(
         [[
+        local max_results = 5
+
         tester.builtin_picker('find_files', 'README.md', {
           post_typed = {
             { %s, function() return #GetResults() end },
@@ -66,9 +69,10 @@ describe("builtin.find_files", function()
           sorter = require('telescope.sorters').get_fzy_sorter(),
           layout_strategy = 'center',
           layout_config = {
-            height = max_results,
+            height = max_results + 1,
             width = 0.9,
           },
+          border = false,
         }, vim.fn.json_decode([==[%s]==])))
       ]],
         expected,