[webpack-plugin-utilities] Add evaluateConstantEstreeExpression

[iclanton]

Summary

Reworks the evaluateAcornNode helper in @rushstack/webpack-plugin-utilities:

• Renamed evaluateAcornNode → evaluateConstantEstreeExpression (the previous name referenced the parser rather than the node shape it operates on).
• Removed the hand-rolled IAcornNode interface in favor of the existing @types/estree types. This surfaced and fixed a few latent correctness gaps that the old any-ish casts hid:
  • object SpreadElements ({ ...other }) are now explicitly rejected instead of silently mis-evaluated,
  • computed / non-identifier property keys are handled via proper narrowing,
  • sparse array holes ([1, , 3]) now evaluate to null instead of being passed into the recursion.
• Expanded supported node types for constant values:
  • UnaryExpression — notably negative numbers like -1, which parse as a unary - applied to a literal and previously threw. Also supports +, !, ~.
  • TemplateLiteral with no ${...} substitutions.
• Added a TSDoc comment describing intended usage (reading literal call arguments inside webpack parser hooks), the supported node types, and limitations.
• Added unit tests covering every supported node type, nesting, sparse holes, and all error paths (computed keys, non-identifier keys, object spreads, unsupported operators / node types). This enables the test phase for the package, which previously had none.
• Updated the hashed-folder-copy-plugin consumer to the new name.

Details

• The package previously had no Jest setup; test / _phase:test scripts were added (the rig already provides the test phase + config).
• All 23 tests pass and the build is clean (API report regenerated).

How it was tested

rush build and rush test for @rushstack/webpack-plugin-utilities, plus a build of the hashed-folder-copy-plugin consumer.