Revisit floating example for IE/Edge

[XhmikosR]

About the floating labels example, I'm a bit confused: there's an old patch for IE that seems to… break the example.

If I remove it, the example works fine in IE11 (tested on BrowserStack, W7 & W10).
However the Edge patch seems required. Both were introduced in #25919, but MDN compatibility table seems clear: IE10 & 11 did support their vendor version.

I'd be in favor of removing it (but should probably be another PR, souldn't it?).

Originally posted by @ffoodd in #30836 (comment)

[XhmikosR]

I haven't checked master BTW.

[ffoodd]

I made 2 PRs:

• Improve the Edge fallback, affects both v5 and v4 (should be backported, Floating labels improvements #30966 )
• Remove the IE fallback, affects only v4 (Floating labels examples in IE #30965 )