ICU-22991 Reduce Calendar object size

[FrankYFTang]

Gregorian monthOfYear, dayOfMonth only need one byte dayOfYear only need two bytes to store.
These fields are used to store calculated value of day of year, day of month and month of year according to Gregorian calendar, and therefore will max to 365, 31 and 12 so it is a waste to store them with 4 bytes. We only need 9 bits, 5 bits, 4 bits for them. We can use bit fields to store but still need 18 bits which is more than 2 bytes. In this PR, I change to use 2 + 1 + 1 = 4 bytes to store them. Save 8 bytes per Calendar object

Checklist

• Required: Issue filed: ICU-22991
• Required: The PR title must be prefixed with a JIRA Issue number. Example: "ICU-1234 Fix xyz"
• Required: Each commit message must be prefixed with a JIRA Issue number. Example: "ICU-1234 Fix xyz"
• Issue accepted (done by Technical Committee after discussion)
• Tests included, if applicable
• API docs and/or User Guide docs changed or added, if applicable

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Notice: the branch changed across the force-push!

• icu4c/source/i18n/calendar.cpp is different
• icu4c/source/i18n/unicode/calendar.h is different

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[markusicu]

optional: Java?

[richgillam]

Looks fine to me. I second both of Markus's comments, but have none of my own to add.

[FrankYFTang]

PTAL

[markusicu]

Whoa! I guess I need to be careful what I ask for... I glanced at many of the changes, and they look plausible, and it looks like you are reducing the amount of work and reducing unused variables. I am stamping.

As for Java, I suspect that it might matter less there whether we store byte/short vs. int, but it might be nice to port the other changes there if they make sense. (Don't know what the Grego functions look like there since Java does not have output reference types.)

@richgillam ok?

[richgillam]

Looked at it again. LGTM.

[jira-pull-request-webhook]

Hooray! The files in the branch are the same across the force-push. 😃

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[FrankYFTang]

optional: Java?

I will deal with that in a separate PR later.