JS: Add parse_int(), to_upper_case(), to_lower_case()

[Spooks4576]

What's new

Added a Global StringUtils Library that gets handled globally also added a ParseInt global function similar to what regular js has

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For the reviewer

• I've uploaded the firmware with this patch to a device and verified its functionality
• I've confirmed the bug to be fixed / feature to be stable

[Willy-JL]

as per mjs docs:

• substring("abc", 1, 3) -> "abc".slice(1, 3)
• slice("abc", 1, 3) -> "abc".slice(1, 3)
• indexOf("abc", "bc") -> "abc".indexOf("bc")
• GetLength("abc") -> "abc".length

as for parse_int("123"), mostly ok, just some tiny changes to error handling, nothing major, well done

toUpperCase("abc") and toLowerCase("ABC") i'd like to have on the string objects themselves. i will see if this can be done easily, if not can keep global (though i will move into js_thread.c, having a separate header which actually contains code, and is labelled as a module when its global, is not ideal.

also, please stick to a naming convention. parseint, parse_int, indexOf and GetLength can't possibly all belong to the same API... considering the existing examples from OFW js runner, i'd say the safe bet is snake_case globals, and camelCase module functions.

[Willy-JL]

adding to string object as "abc".toUpperCase() would go into getprop_builtin_string() of lib/mjs/mjs_exec.c, which means it would end up in firmware flash. i'd rather have it in js_app, so its in fap instead. ill make it respect the global function naming scheme as to_upper_case("abc")