Propose to remove support for CompactStrings off

[wenshao]

Initially, the option to disable CompactStrings was provided for performance 
reasons. 
However, with some optimizations for UTF8 scenarios and Latin1, disabling 
CompactStrings no longer has any performance benefits. I propose removing the 
related code to make it simpler and easier to maintain.
I've submitted a draft Pull Request ( https://github.com/openjdk/jdk/pull/27988 
<https://github.com/openjdk/jdk/pull/27988 > ) and would appreciate your 
feedback.
-
Shaojin Wen