Better error reporting for incomplete values

[gotwarlost]

• Currently we descend into expressions to find the parts that are incomplete and reporting these. This is already a huge step over saying something in this resource is incomplete, figure it out
• However since we evaluate locals eagerly we cannot descend into expressions assigned to local variables
• Separately, if a variable foo is incomplete and used in 3 places in an expression we report it 3 times

Figure out a way to make this better.

Also some parts of the code do a poor job with diags capture. Maybe simplify and standardize this across the board.