automatically promote primitive types to objects when necessary

[zxul767]

Currently there is a difference between primitive types (i.e., numbers, booleans and strings) and objects, as far as their representation goes. this prevents primitive types from having methods (e.g., we cannot say "string".length())

while it is desirable to keep primitives as lightweight as possible (e.g., to avoid costly overhead when holding collections of them), it is also quite convenient to be able to write expressions such as "string".ends_with("ing") instead of string__ends_with("string", "ing").

we should explore the possibility of having an expression such as:

"string".starts_with("str")

be equivalent to:

str("string").starts_with("str")

where str(.) is the cast operator (or alternatively, the str class constructor overloaded for various types) that returns an object.

while it might also be desirable to do something similar for numbers and booleans, the need is much less clear (e.g., writing 12.sin() or (-12).abs() adds no more clarity than their usual counterparts sin(12) and abs(-12); on the contrary, they are arguably less clear.)

[zxul767]

the implementation for string literals is now in main for jlox (clox needs to catch up right after the PR for adding list is done)