docs: add array shorthand syntax T[] documentation and changelog

- Update arrays-and-hashes docs with `String[]` syntax examples (en, ja, ko)
- Update built-in-generics with array shorthand examples
- Add v0.0.43 to changelog with array shorthand feature
- Update cheatsheet with new syntax
- Update optional-rest-parameters examples
- Both `String[]` and `Array<String>` syntaxes are documented

Author: yhk1038

docs/learn/basics/basic-types.md

@@ -175,7 +175,7 @@ speed_of_light: Float = 2.998e8  # 299,800,000
 ### Float Arithmetic
 
 ```trb title="float_math.trb"
-def calculate_average(values: Array<Float>): Float
+def calculate_average(values: Float[]): Float
   sum = 0.0
   values.each do |v|
     sum += v