fix: let charts in auto-height containers grow back after shrinking (…

[gbosetti]

Fix attempt for #12251

Before / bug	After / fix
bug.mov	fix.1.mov
The chart was sizing itself against its container's height. With no fixed height, the container is just as tall as the chart, so the chart kept comparing against its own previous size: shrinks went through, growth never did.	It now ignores the container's height when that height is only the chart's own, so it follows the container both ways.

Videos recorded on the docs animations page (the "Looping tension" example), served from a local build.

Notes

• This is not just about zoom. It happens at devicePixelRatio 1 too — zoom just makes people resize more, so they notice it.
• The clamp comes from fix: respect aspect ratio with container height #10646, which is right for containers with a fixed height. Those keep working the same way.

Tests

test/specs/issue.12251.tests.js — 5 specs: grow and shrink at DPR 1 and 1.35, repeated identical resizes, a looping animation, and a shrink-then-grow drag. They fail on master and pass with this change. The existing helpers.dom, platform.dom and core.controller suites (including the #10646 / #10693 fixed-height cases) still pass, in Chrome and Firefox.