LogLevelText extension
LogLevel 的展示文本 / Display text for LogLevel
单一实现：此前 LogEntry.levelText 与 ExportService 里各有一份同样的
switch，新增级别时极易漏改其中一处。
Single implementation: LogEntry.levelText and ExportService each had a
copy of the same switch, so adding a level risked missing one.
- on
Static Methods
-
of(
LogLevel level) → String -
Available on LogLevel, provided by the LogLevelText extension
级别缩写（V / D / I / W / E）/ Level abbreviation (V / D / I / W / E)