Metaprogramming shenanigans and other fixes

[savq]

Literals

• Allow literals in quote and interpolation expressions.
• Allow strings and prefixed strings in field_expression RHS.
• Replace true and false with boolean_literal.
• Allow backslash to escape any character (that's how command_literal works).
• Define escape_sequence as a constant, not a grammar rule (to parse character_literal as a single token).
• Add string and command suffixes.
• Refactor float_literal.

Identifiers and operators

• Refactor quote_expression.
• Add syntactic operators to quote_expression (e.g. :.).
• Define constants for lazy logic operators.
• Split adjoint_expression from unary_expression.
• Add more math symbols to identifier.
• Allow begin as an identifier.
• Allow parenthesized identifier/operators in more places.

Primary expressions

• Refactor quote_expression.
• Add curly_expression and _immediate_brace rule to scanner (for macro DSLs).
• Allow interpolation_expression in more places.
• Replace scoped_identifier with field_expression in function names. Function names already allow interpolations, so allowing more primary expressions isn't that bad. (e.g. function $M.$f(x) end).

Juxtapositions

• Rename coefficient_expression to juxtaposition_expression.
• Allow any _primary_expression in RHS of juxtaposition_expression.

tuples and function arguments

• Allow arbitrary expressions in named tuples and keyword arguments.
• Allow mixing expressions and named fields in tuples.
• Allow call_expression in parameter list (for Gen.jl).

Assignments

• Define let_binding in terms of named_field.
• Allow assignments in return_statement.
• Allow simple bindings (named fields) in arrays and string_interpolation.
• Allow declarations in parenthesized_expression.
• Allow nested named fields.
• Allow quote_expression in assignments' LHS.
• Parse .= as compound_assignment_expression, not assignment.
• Allow typed_parameter in for_binding.
• Allow _declaration in macro_argument_list.

Tests

• Remove Mocha.jl. It's been deprecated since 2018.
• Update repo versions
• Add Pluto.jl as an example repo. Pluto:
  • Is currently the most popular Julia project on github
  • Is a large Julia Project (20kloc)
  • Uses a lot of metaprogramming
  • Uses a lot of emojis

---

• Closes #7
• Closes #35
• Closes #84

This PR has two goals:

• Adding things I missed in #83.
• Improving the way the grammar handles metaprogramming, DSLs and some questionable practices.

While it doesn't stand out, one of the most important changes is the extension of valid juxtapositions. tree-sitter has very poor support for explicit whitespace handling, so like in other whitespace sensitive cases, this is a best-effort approximation. It also results in a much more bloated src/parser.c.