Post-restore -Xshareclasses change semantics

[dsouzai]

This issue tracks what changes can be made via the -Xshareclasses option post-restore. For 0.38, the plan is to introduce -Xshareclasses:disableOnRestore [1] which is a best effort implementation to disable the SCC, and can only be specified post restore [2].

Post 0.38, Some reasonable changes to support may be

• -Xshareclasses:none to -Xshareclasses:... and vice versa
• Adding verbose post-restore
• Modifying sizes via the -Xsc* variants

VM Changes

TBD

JIT Changes

Most changes to -Xshareclasses/-Xsc* don't impact the JIT as all interactions with the SCC are done via APIs. Adding -Xshareclasses:none post-restore is trivial to implement (it is essentially the same work needed to implement -Xshareclasses:disableOnRestore); doing the opposite will be more work and boils down to implementing #16865.

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[1] #16714 (comment)
[2] #16714 (comment)

[dsouzai]

@tajila @vijaysun-omr feel free to update the main description as needed.
@hangshao0 fyi.

[hangshao0]

FYI @ehrenjulzert