Offer to format data sizes in either IEC or SI.

Add flags to let callers specify if they want IEC (power-of-two) or
SI (power-of-ten) units when formatting bytes.

Continue using SI units by default, since certain folks seem to have
strong opinions about that.

Bug: 76159924
Test: atest android.text.format.FormatterTest
Exempt-From-Owner-Approval: previous PS approved
Change-Id: I0074bb2578c2230e938b3f39c2564b1083feb825