use ESM module syntax & minor cleanups

The biggest change here is moving various element classes under
more scope-specific directories, which helps to avoid circular
dependencies and is just cleaner to navigate and expand in the
future.

Otherwise this is a largely uncritical port to ESM module syntax!
There are probably a number of changes and other cleanups that
remain much needed.

Whenever I make changes to tui-lib it's hard to believe it's
already been <INSERT COUNTING NUMBER HERE> years since the
previous time. First commits are from January 2017, and the
code originates a month earlier in KAaRMNoD!

1 files changed, 13 insertions, 0 deletions

diff --git a/ui/presentation/HorizontalBox.js b/ui/presentation/HorizontalBox.js
new file mode 100644
index 0000000..d396ec3
--- /dev/null
+++ b/ui/presentation/HorizontalBox.js
@@ -0,0 +1,13 @@
+import {DisplayElement} from 'tui-lib/ui/primitives'
+
+export default class HorizontalBox extends DisplayElement {
+  // A box that will automatically lay out its children in a horizontal row.
+
+  fixLayout() {
+    let nextX = 0
+    for (const child of this.children) {
+      child.x = nextX
+      nextX = child.right + 1
+    }
+  }
+}