Improve error messages, fix naming bug and assignment bug in native

[openorclose]

Fixes source-academy/frontend#963

When js functions throw their own errors (e.g. head(xs) will throw if xs is not a pair), it gets wrapped in an ExceptionError. If these functions are nested down, they each get wrapped in their own ExceptionError, causing the [object Object] error message.

Now, we check whether the error has already been wrapped before wrapping the error.

This also improves many of the Line -1 messages that occur.

This also fixes the bug here: https://sourceacademy.nus.edu.sg/playground#chap=3&exec=1000&ext=NONE&prgrm=GYVwdgxgLglg9mABAdwE4EMAOAKAlIgbwChFTEiBfIA

and the bug here:

https://sourceacademy.nus.edu.sg/playground#chap=3&exec=1000&ext=NONE&prgrm=DYUwLgBAhhC8EAcoEsBOBuAUDeS3qA

[coveralls]

Pull Request Test Coverage Report for Build 1792

• 16 of 16 (100.0%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 88.906%

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Totals
Change from base Build 1770:	0.1%
Covered Lines:	2188
Relevant Lines:	2397

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💛 - Coveralls

[chrisgzf]

can this be merged soon? many students are facing the [object Object] errors on piazza

EDIT: fixed