Query validation of literal, regexp, and structural search patterns

Created by: rvantonder

Literal search

Add and test the combination of literal search patterns (which are not validated against any syntax properties) are appropriately validated alongside general search parameters like repo:, that do require validation.

Regexp search

Validate that concatted regexp patterns compile. Validate that parentheses are appropriately disambiguated (see #9170 (closed))

Structural search

Validate that parentheses and quotes are balanced for respective languages.