Object#duplicable?
1. Improve tests
2. Remove unnecessary constant
3. Add docs for BigDecimal#duplicable?
Merge pull request #14733 from akshay-vishnoi/test-cases

Improve tests for duplicable, remove unnecessary constant
[ci skip] Avoid suggesting dangerous code in i18n guide

Calling `to_sym` on user input opens apps up to Denial of Service attacks, via the symbol table being expanded to consume vast swathes of memory.

It is a fairly common configuration to have DNS configured such that all subdomains route to your Rails app, in which case an attacker visits `www1.foo.com`, `www2.foo.com`, and so on until something gives.

It is far less likely to have this problem with TLDs, so that change was only for consistency.
Merge pull request #14770 from crazymykl/avoid_dos_vuln_in_i18n_guide

Avoid suggesting dangerous code in i18n guide
SQL Like escaping helper method. [Rob Gilson & Yves Senn]

Closes #14222.

This is a follow up to #6104

This does not have the backwards compatibility issues brought up in
implementation to break.
Changed the NullRelation so that when count is called with #group it will properly return an empty hash instead of zero. Fixes issue #14721

Conflicts:
	activerecord/CHANGELOG.md