Fix selected text background in toykonight (#9789)

Before the fix, the color that the original (Neovim) tokyonight uses for
Neovim's visual mode was used in Helix for highlighting the selected
item in the picker. But for the highlighting of selected _text_ in
Helix (corresponding to Neovim's visual mode), a much darker background
was used. This made it very hard to pick out selected text, in
particular in suboptimal lighting conditions.

I swapped the two colors, so that text selection now looks like in
Neovim, while selected items in the picker are highlighted a bit less
strongly. (But still easy to see because the whole line is highlighted.)

runtime/themes/tokyonight.toml

@@ -76,15 +76,15 @@ hint = { fg = "hint" }
 "ui.menu" = { bg = "bg-menu", fg = "fg" }
 "ui.menu.selected" = { bg = "fg-selected" }
 "ui.popup" = { bg = "bg-menu", fg = "border-highlight" }
-"ui.selection" = { bg = "bg-highlight" }
-"ui.selection.primary" = { bg = "bg-highlight" }
+"ui.selection" = { bg = "bg-selection" }
+"ui.selection.primary" = { bg = "bg-selection" }
 "ui.statusline" = { bg = "bg-menu", fg = "fg-dark" }
 "ui.statusline.inactive" = { bg = "bg-menu", fg = "fg-gutter" }
 "ui.statusline.normal" = { bg = "blue", fg = "bg", modifiers = ["bold"] }
 "ui.statusline.insert" = { bg = "light-green", fg = "bg", modifiers = ["bold"] }
 "ui.statusline.select" = { bg = "magenta", fg = "bg", modifiers = ["bold"] }
 "ui.text" = { bg = "bg", fg = "fg" }
-"ui.text.focus" = { bg = "bg-visual" }
+"ui.text.focus" = { bg = "bg-focus" }
 "ui.text.inactive" = { fg = "comment", modifiers = ["italic"] }
 "ui.text.info" = { bg = "bg-menu", fg = "fg" }
 "ui.virtual.ruler" = { bg = "fg-gutter" }
@@ -126,6 +126,6 @@ border = "#15161e"
 border-highlight = "#27a1b9"
 bg = "#1a1b26"
 bg-inlay = "#1a2b32"
-bg-highlight = "#292e42"
+bg-selection = "#283457"
 bg-menu = "#16161e"
-bg-visual = "#283457"
+bg-focus = "#292e42"