Add Treesitter Context package

Shows a line for the containing class and function when they don't fit
on the screen.

lua/custom/plugins/nvim_treesitter_context.lua

@@ -0,0 +1,20 @@
+return {
+	'nvim-treesitter/nvim-treesitter-context',
+	config = function ()
+		require('treesitter-context').setup {
+			-- See options here: https://github.com/nvim-treesitter/nvim-treesitter-context?tab=readme-ov-file#configuration
+			enable = true,      -- Enable this plugin (Can be enabled/disabled later via commands)
+			max_lines = 0,      -- How many lines the window should span. Values <= 0 mean no limit.
+			min_window_height = 0, -- Minimum editor window height to enable context. Values <= 0 mean no limit.
+			line_numbers = true,
+			multiline_threshold = 20, -- Maximum number of lines to show for a single context
+			trim_scope = 'outer', -- Which context lines to discard if `max_lines` is exceeded. Choices: 'inner', 'outer'
+			mode = 'cursor',    -- Line used to calculate context. Choices: 'cursor', 'topline'
+			-- Separator between context and content. Should be a single character string, like '-'.
+			-- When separator is set, the context will only show up when there are at least 2 lines above cursorline.
+			separator = nil,
+			zindex = 20, -- The Z-index of the context window
+			on_attach = nil, -- (fun(buf: integer): boolean) return false to disable attaching
+		}
+	end
+}