Add method to parse the size in FileUtils

The method parseSize() will parse the strings that match
the regular expression:

  "^((\\s*[-+]?[0-9]+)\\s*(B|K|KB|M|MB|G|GB|Ki|KiB|Mi|MiB|Gi|GiB)\\s*)$"

For example: 12GB, +100MB, 23MiB.

It will return the size in bytes.

Test: atest
Bug: 231718727
Change-Id: Id4b9084d2ff8a0a8bd23ddb8a7e10dcf17391c49