Unify `--filesize` and `--statement-size` definition with mydumper's

[lichunzhu]

Feature Request

Is your feature request related to a problem? Please describe:

Currently dumpling's --filesize and --statement-size only counts the column values' size. However, mydumper counts the text file's size, which may confuse users.

Describe the feature you'd like:

Unify --filesize and --statement-size definition with mydumper's which means sentences like 'INSERT' are also counted in filesize.

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Optimization:

[lichunzhu]

@kennytm WDYT?

[kennytm]

👍