IDL: Implement float/double correctly

Specifically, do not require the [TypeChecking=Unrestricted] extended
attribute for correct behavior.

This renders the [TypeChecking=Unrestricted] extended attribute
ineffective, meaning we can then drop it from actual IDL files without
code generation changes.

BUG=354298

Review URL: https://codereview.chromium.org/970843002

git-svn-id: svn://svn.chromium.org/blink/trunk@191108 bbb929c8-8fbe-4397-9dbb-9b2b20218538
9 files changed