HashWithIndifferentAccess#dup doc [ci skip]

The phrase "exact copy" in the existing docmentation is somewhat
misleading.
Merge pull request #15440 from ilikepi/pr_docs_activesupport_hwia_dup

HashWithIndifferentAccess#dup doc [ci skip]
Merge pull request #15437 from sgrif/sg-missing-test-case

Add missing test case for writing unknown attributes
Clear all caches calculated based on `@columns` when `@columns` changes
Update documentation for setting asset_host to a Proc, mention that the request parameter might not be supplied [ci skip]
[ci skip] Correct documentation of HashWithIndifferentAccess#dup
Merge pull request #15445 from krautcomputing/fix_asset_host_docs

Update documentation for setting asset_host to a Proc [ci skip]
Merge pull request #15446 from akshay-vishnoi/doc_changes

[ci skip] Correct documentation of HashWithIndifferentAccess#dup
Tiny formatting fix in AS change log [ci skip]
Test `except!` in other cases too
Merge pull request #15434 from sgrif/sg-clear-caches

Clear all caches calculated based on `@columns` when `@columns` changes
[ci skip] Correct output of Hash#symbolize_keys
Merge pull request #15448 from akshay-vishnoi/doc_changes

[ci skip] Correct output of Hash#symbolize_keys
Fix AS::NumberHelper results with rationals

:precision was incorrectly being applied to Rationals

before:
  ActiveSupport::NumberHelper.number_to_rounded Rational(10, 3), precision: 2
  => "3.3"
after:
  ActiveSupport::NumberHelper.number_to_rounded Rational(10, 3), precision: 2
  => "3.33"
[ci skip] correct doc for ActionView::Helpers::DebugHelper
Missing period from AP/CHANGELOG [ci skip]
Merge pull request #15449 from aditya-kapoor/correct-debug-doc

[ci skip] correct doc for ActionView::Helpers::DebugHelper
Removed 'Caching with Rails' guide from WIP, this guide isn't ready to
be published and requires more attention. [ci skip]
config.assets.digests -> config.assets.digest

in Asset Pipeline guide.

[skip ci]
Merge pull request #15456 from jonatack/patch-7

config.assets.digests -> config.assets.digest