Refactor bool exp synthesizer

It's now more intelligent about generating IS NULL clauses. For example,
instead of 'LOWER(param) IS NULL' it now generates 'param IS NULL'.

npm-shrinkwrap.json

@@ -3003,12 +3003,9 @@
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@@ -3854,12 +3851,6 @@
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@@ -10612,6 +10603,12 @@
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       "dev": true
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