feat(overrides): Add additional prefix/suffix support

Allows a higher-level prefixes and suffixes by allowing it directly on
`@theme-*` options, which are what are set directly against Tmux's
options.

These are the prefix/suffix options added:

- `@theme-status-left-prefix`
- `@theme-status-left-suffix`
- `@theme-status-right-prefix`
- `@theme-status-right-suffix`
- `@theme-window-status-current-prefix`
- `@theme-window-status-current-suffix`
- `@theme-window-status-prefix`
- `@theme-window-status-suffix`

As they are applied on the highest level, it means they work on ALL
themes, including the `default` theme.

The `@themepack-*` prefix/suffix options still work too, but only for
themes that uses them and have three separate text areas on the left and
right status.

test/default_test.go

@@ -44,3 +44,34 @@ func TestDefaultTheme(t *testing.T) {
 		"status-style":                "fg=black,bg=green",
 	})
 }
+
+func TestDefaultThemeOverrides(t *testing.T) {
+	name := "default"
+	filename := "../" + name + ".tmuxtheme"
+
+	tmuxSetup()
+
+	out, err := tm.Exec("source-file", "theme-overrides.conf")
+	assert.NoErrorf(t, err, `%s: Failed to load overrides: %s`, name, out)
+
+	out, err = tm.Exec("source-file", filename)
+	assert.NoErrorf(t, err, `%s: Failed to load theme: %s`, name, out)
+
+	opts, err := tm.GetOptions(tmux.GlobalSession)
+	assert.NoError(t, err)
+
+	assertHasPrefix(t, opts["status-left"], "SLP=")
+	assertHasSuffix(t, opts["status-left"], "=SLS")
+	assertHasPrefix(t, opts["status-right"], "SRP=")
+	assertHasSuffix(t, opts["status-right"], "=SRS")
+
+	opts, err = tm.GetOptions(tmux.GlobalWindow)
+	assert.NoError(t, err)
+
+	assertHasPrefix(t, opts["window-status-current-format"], "WSCP=")
+	assertHasSuffix(t, opts["window-status-current-format"], "=WSCS")
+	assertHasPrefix(t, opts["window-status-format"], "WSP=")
+	assertHasSuffix(t, opts["window-status-format"], "=WSS")
+
+	tmuxTearDown()
+}