* csp: warn legacy browsers that do not support CSP
The new csp.warnLegacyBrowsers configuration is enabled by default, and
it shows a warning message to any legacy browser when they access Kibana
to indicate that they are not enforcing the basic security protections
of the current install.
The protections check is the same as csp.strict, so this feature is
designed to be used as an alternative to aid in BWC. When csp.strict is
enabled, warnLegacyBrowsers is effectively ignored.
* fix ChromeService tests
* more test fixes
* csp injectvars in legacy test bundle
* update warning text and make it translatable
* no need to warn in legacy browser unit tests
* tests for chrome legacy browser warning
* document legacy browser warning breaking change
* update csp warning toast message
* add period, remove dev code
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