Update CodeMirror to 5.62.2
Update CodeMirror to 5.62.2

This fixes an issue on mobile where typing causes the keyboard line to go out of sync (e.g. the thing showing where your keyboard is on
the text box is at the start even though you're typing to the right of
some words.

This issue looks like it was fixed in 5.61.1 but we may as well update to
the latest version.

Change-Id: I4c05ad02e18bec59fc390d6f4118ef42eaa5fd66

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