[HUDI-8464] Minor cleanup of time generation APIs and locking

[vinothchandar]

Change Logs

• Removed one createNewInstantTime() API from BaseHoodieClient.
• Fixed tests using them.
• Renaming TimeGenerator APIs and classes to be more intuitive

Impact

none

Risk level (write none, low medium or high below)

none

Documentation Update

none

Contributor's checklist

• [ ] Read through contributor's guide
• [ ] Change Logs and Impact were stated clearly
• [ ] Adequate tests were added if applicable
• [ ] CI passed

[hudi-bot]

CI report:

• 2491d7741e372ec2580bf00cf8f60045cac8a24e Azure: SUCCESS

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