Change ConvertForLoopOperation to avoid getting type from size() method

[jjohnstn]

• change ConvertForLoopOperation to change the logic that gets the type of size() method call to instead get the type of the expression calling it
• fixes #1617

What it does

See issue.

How to test

Run JDT UI test suite and test with jdtls.

Author checklist

• [x] I have thoroughly tested my changes
• [x] The change is following the coding conventions
• [x] I have signed the Eclipse Contributor Agreement (ECA)

[mickaelistria]

I confirm this patch fixes https://github.com/eclipse-jdtls/eclipse-jdt-core-incubator/issues/748 , thank you!

[jjohnstn]

@mickaelistria Great. I'll merge it for 4.34 M1 when the branches open.