Handle decorations better in some optimizations (#2716)

There are a couple spots where we are not looking at decorations when we should.

1. Value numbering is suppose to assign a different value number to ids if they have different decorations.  However that is not being done for OpCopyObject and OpPhi.

1. Instruction simplification is propagating OpCopyObject instruction without checking for decorations.  It should only do that if no decorations are being lost.

Add a new function to the decoration manager to check if the decorations of one id are a subset of the decorations of another.

Fixes #2715.