fix mysql version check in rename_index

also clarify native rename_index support is >= 5.7, not > 5.7
Merge pull request #13093 from ccutrer/fix-mysql-version-check

fix mysql version check in rename_index
Remove `DatabaseStatements#case_sensitive_equality_operator`. It has been deprecated already.
#type_cast - improve performance & readability
Checking no debugger on JRuby

fixes tests for JRuby
updating  options documentation for associations
removed unnecessary test case and improved test case for belongs_to having invalid  options
Merge pull request #13100 from akshay-vishnoi/f-refactor

#type_cast - improve performance & readability
Merge pull request #13099 from kamipo/remove_case_sensitive_equality_operator

Remove `DatabaseStatements#case_sensitive_equality_operator`. It has been deprecated already.
Merge pull request #13095 from kuldeepaggarwal/test-case-updation

removed unnecessary test case
Remove unused variable

This method is not using the block variable directly since it is calling
yield
Typo fix
Merge pull request #13102 from akshay-vishnoi/typo

Typo fix
Fix URL to robots.txt documentation
Merge pull request #13097 from arunagw/jruby-test-fixes

Skipping debugger inclusion test if JRuby
Merge pull request #13104 from christophemaximin/fix_robots_txt_link

Fix URL to robots.txt documentation [ci skip]
Improve Module#delegate documentation to tell that delegate don't work with private or protected methods. [ci skip]
Merge pull request #13092 from laurocaetano/improve_documentation_for_delegate

Improve Module#delegate documentation.
add missing arel dependency to `active_record_master` bug report script.

[ci skip].

This solves:

```
Could not find gem 'arel (~> 5.0.0) ruby', which is required by gem 'rails (>= 0) ruby', in any of the sources.
```
Fixes failing test for JRuby

in JRuby FileUtils do not change
current dir when moving files
Merge pull request #13105 from arunagw/jruby-gen-test-fix

Fixes failing test for JRuby