[rush] Support percentage-based weights for operationSettings in rush-project.json

[LPegasus]

Summary

Add issue #5607 proposal 1 feature.

Details

• WeightedOperationPlugin: Added a function to convert weight settings in RushProjectConfiguration.operationSettings percentage string to integer based on os.availableParallelism().
• WeightedOperationPlugin.test.ts: Added some tests.
• RushProjectConfiguration.ts: Updated IOperationSettings.weight type definition.
• rush-project.schema.json: Updated weight field json schema.
• If the calculated result of the specified percentage has decimals, use Math.floor to round down to an integer. Maximize CPU utilization as much as possible.

How it was tested

• Add unit test cases.
• Tested in my test rush repo.

Impacted documentation

None