Spring SpEL's CompoundExpression.toStringAST() incorrectly includes . for indexed properties

I discovered this bug while writing tests for gh-30580.

https://github.com/spring-projects/spring-framework/blob/aa2a0674893ecf72ea6c8e662f28df7813e5b2e5/spring-expression/src/test/java/org/springframework/expression/spel/ParsingTests.java#L74

Essentially, an expression like property1[0].property2['key'].methodOne() should have an identical AST string representation; whereas, the current AST string representation is property1.[0].property2.['key'].methodOne() with a . preceding every indexed property access.