The possible metrics names are relatively fixed in an OAP run, we previously always escape the metrics names, building a new regex Pattern from scratch, which is cpu-consuming.
In this patch, I cache the escaped metrics names, and if it missed, use a pre-compiled regex Pattern to escape the metrics name.
This patch also replace string concatenation `+` with `StringBuilder` in generated classes, which won't get optimized by Java compiler
This may reduce 1~1.5 vCPU under 20K RPS environment.
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