Reduce the number of global functions by moving it to instance method
`FileInfo::generateArgInfoCode()`.
In the process, make the following parts of `FileInfo` private:
- `$funcInfos`
- `$generateFunctionEntries`
- `$declarationPrefix`
- `$generateClassEntries`
- `$generateCEnums`
- `::getMinimumPhpVersionIdCompatibility()`
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