[Testing guide] Use "Fixtures API" instead of "fixture api".
[Testing guide] Using "Fixtures API" consistently

- In guides, "API" is used consistently instead of "api".
- Reason behind replacing "fixtures API" to "Fixtures API" is because
  here we are referring to the concept of "fixtures". In other places in
  the guide "fixture" OR "fixtures" is referred to the single or
  multiple instances of test data.
- This is also followup of https://github.com/rails/docrails/commit/aa9d1332b20305dd860b21a7ada06c5252bebad5#commitcomment-8497376.
Fix grammar on ActiveRecord::AttributeMethods doc.

[ci skip]
Merge branch 'master' of github.com:rails/rails
Add docs for AS::TimeWithZone + and -

The example was taken from the commit message 676d6a6.

[ci skip]
Merge branch 'document-time-with-zone-plus-and-minus'
Better doc for AS::DateTime#seconds_since_midnight

Adds examples and keeps coherent with the documentation of the
similar method `seconds_until_end_of_day`. [ci skip]
[ci skip] Fix output of video_tag helper
Improving tips about installation in the guides [ci skip]
Pass connection rather than alias_tracker

Because we're only using the `connection` so passing the entire tracker
isn't unnecessary.

Eventually only the `connection` will be passed to `add_constraints`
with later refactoring but curretly that's not possible because of
`construct_tables` method.
Fix handling of positional url helper arguments when format is false

There is no need to subtract one from the path_params size when there is
no format parameter because it is not present in the path_params array.

Fixes #17819.
Merge pull request #18020 from binaryberry/handle-positional-args-with-format-false

Fix handling of positional url helper arguments when format is false
Merge pull request #18019 from eileencodes/pass-connection-rather-than-alias_tracker

Pass connection rather than alias_tracker
ParameterFilter shouldn't try to dup symbol keys
allow URL helpers to work with optional scopes
Merge pull request #18021 from nateberkopec/fix-filter-param-symbol-dup

ParameterFilter shouldn't try to dup symbol keys
Merge pull request #18022 from agrobbin/url-helpers-optional-scopes

Allow URL helpers to work with optional scopes
Re-enable capture'ing non-String values

This has been discussed in #17661 and partially reverts the changes made
in 9de83050d3a4b260d4aeb5d09ec4eb64f913ba64 and 986cac73e3c56b3dfa22fd1464f6913e38d32cc3

The test case added to content_for acts as a regression / acceptance test.
Merge pull request #18024 from carpodaster/fix/actionview/capture-non-strings

Re-enable capture'ing non-String values
Fix Duplicate web-console entries in Gemfile