RFR: 8323083: [GenShen] Alloca avoidance, const-safety, interface decluttering in promotion budgeting [v2]

[Y. Srinivas Ramakrishna]

> 8323083: [GenShen] Alloca avoidance, const-safety, interface decluttering in promotion budgeting

Y. Srinivas Ramakrishna has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 14 commits:

 - Merge branch 'master' into couple_sizing_tenuring
 - More consts and a bit more encapsulation of preselected regions.
 - Refactor to make interface narrow since state is implicitly managed in
   collection_set. Further clean up can wait for the future.
 - Replace automatic array variables with resource area allocated arrays
   and coupled resource marks.
 - Replace alloca() with automatic array allocation. Might be better to
   replace with resource arrays for hygiene.
 - Structured maintenance of preselected regions field: first iteration
 - Some more documentation comments.
 - Add/expand some documentation comments; remove some unused "tracking
   variables".
 - Remove unnecessary `num_regions` parameter to method
   `select_aged_regions()`.
 - Merge branch 'master' into couple_sizing_tenuring
 - ... and 4 more: https://git.openjdk.org/shenandoah/compare/2d4761d0...d8b98081

-------------

Changes: https://git.openjdk.org/shenandoah/pull/381/files
 Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=381&range=01
  Stats: 164 lines in 6 files changed: 91 ins; 26 del; 47 mod
  Patch: https://git.openjdk.org/shenandoah/pull/381.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/381/head:pull/381

PR: https://git.openjdk.org/shenandoah/pull/381