Fix #25083: Allow bracket notation for enum keys in computed properties

This commit fixes an issue where using bracket notation to access enum
members (e.g., Type['key']) was not accepted in computed property names
of type literals, even though dot notation (e.g., Type.key) worked fine.

The problem was in the isLateBindableAST function in checker.ts, which
only accepted EntityNameExpression. Element access expressions like
Type['key'] were rejected even though they resolve to the same literal
type as their dot notation equivalents.

Changes:
- Modified isLateBindableAST to accept ElementAccessExpression when the
  base object is an EntityNameExpression
- This enables bracket notation for accessing enum members with
  non-identifier names (e.g., '3x14' or names starting with digits)
- Added comprehensive test case covering various scenarios including
  identifier and non-identifier enum keys with bracket notation

Fixes #25083

Signed-off-by: Rodrigo Sanchez <Rodrigo@sanchezdev.com>

Author: RodrigoSanchezDev