Don't send SameSite=None to incompatible browsers

See merge request gitlab-org/gitlab!40667

The browser gem is quite inefficient for checking SameSite
compatibility. If we rewrite the checks, we see much better performance:

```
Warming up --------------------------------------
            no check    46.338k i/100ms
               check    21.325k i/100ms
Calculating -------------------------------------
            no check    446.012k (± 5.5%) i/s -      2.224M in   5.003135s
               check    210.757k (± 2.8%) i/s -      1.066M in   5.062987s

Comparison:
            no check:   446012.3 i/s
               check:   210756.9 i/s - 2.12x  (± 0.00) slower
```

We set `SameSite=None` in GitLab 12.10 via
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/28205 because
Chrome v80, rolled out in March 2020, treats any cookies without the
`SameSite` directive set as though they are `SameSite=Lax`
(https://www.chromestatus.com/feature/5088147346030592). This is a
breaking change from the previous default behavior, which was to treat
those cookies as `SameSite=None`.

However, older browsers (e.g. MacOS 10.14 on Safari 13.0.3) may
interpret the `None` as `Strict`, which causes users that click on
gitlab.com links from third-party sites (e.g. Gmail, Slack) to log in
again.

https://www.chromium.org/updates/same-site/incompatible-clients
recommends a set of regular expressions to determine whether to send
this. This commit implements most of the logic but skips one case since
this doesn't seem common: macOS 10.14 with an embedded WebKit
browser. This is also what
https://rubygems.org/gems/rails_same_site_cookie does.

I considered using that gem
(https://gitlab.com/gitlab-org/gitlab/-/merge_requests/40663), but I
didn't like how it added another dependency (`user_agent_parser`) that
loads a large YAML database
(https://github.com/ua-parser/uap-ruby#the-pattern-database).

Unit test report docs polishing

See merge request gitlab-org/gitlab!40765

- remove redundant section header "Use cases"
- add in link to JUnit report format

Fix typo on CI CD template docs

See merge request gitlab-org/gitlab!40720

Fix bug in seed fixture to create self monitoring project

See merge request gitlab-org/gitlab!40784

Add Feature Flags search shortcut when feature enabled

See merge request gitlab-org/gitlab!40578

- makes the navigation to Feature Flags more convenient
- makes the Feature Flags sub nav element more findable

Render markdown attribute definitions as tooltips

See merge request gitlab-org/gitlab!40541

Fix vulnerability comment delete button spinner position

See merge request gitlab-org/gitlab!40681

Add kubernetes_agents usage metric

See merge request gitlab-org/gitlab!40559

Docs: Add locked projects troubleshooting note back to ES doc

See merge request gitlab-org/gitlab!40522

Change term Advanced Syntax Search to Advanced Search Syntax

Closes #241787

See merge request gitlab-org/gitlab!40660

Copy CI secrets when retrying a job [RUN AS-IF-FOSS]

Closes #218746

See merge request gitlab-org/gitlab!40458

RUN AS-IF-FOSS Fix group search users scope times out

See merge request gitlab-org/gitlab!38701

Remove file_name and content from snippet mutations

See merge request gitlab-org/gitlab!40727

Docs: Update documentation MR description template

See merge request gitlab-org/gitlab!40403

Add endpoint to update DAST Scanner Profile

See merge request gitlab-org/gitlab!40208

Upgrade guard to 2.16.2

See merge request gitlab-org/gitlab!40710

Rename `status_issue` tag to `testcase` 3 of 3

See merge request gitlab-org/gitlab!40676

Merge branch '232465-mlunoe-share-filter-store-module-between-code-review-and-value-stream-analytics' into 'master'

Refactor(Analytics): introduce store filter module

Closes #232465

See merge request gitlab-org/gitlab!40004

Use the common store filter module for both
Code Review Analytics filter bar
Value Stream Analytics filter bar

This streamlines the filter bar store module and
prepares it to be used for the rest of analytics

Handle `select_one` queries in database load balancing

See merge request gitlab-org/gitlab!40616

Migrate deprecated create issue button in epic tree form

Closes #219817

See merge request gitlab-org/gitlab!40647

Remove pipeline_id column from requirements_management_test_reports

See merge request gitlab-org/gitlab!38924

Removes batch diffs feature flag

See merge request gitlab-org/gitlab!40493

that is no longer used

Prevent Download For Failed Vulnerability Export Jobs

Closes #220601

See merge request gitlab-org/gitlab!40656

In this commit, the file_name and content params are
removed from the snippet mutations

[ci skip]

[ci skip]

Rename feature flag to instance_statistics

See merge request gitlab-org/gitlab!40723

Use UNLINK to remove old repository set caches

See merge request gitlab-org/gitlab!40719