Adopt and enforce new `WP_CLI_CS` standard about doctor-command

[jrfnl]

I've done the prep work to implement this and am left with 9 issues for which I'd like the opinion of one of the maintainers of this package on how to solve this. /cc @schlessera

• 5 issues related to whether or not some (protected, not private) properties should be safe to rename.
• 4 issues about strict comparisons - I know how to change it, but can't easily determine whether these would be safe to change without tracing through the code extensively, which is why I'm asking if someone has a quick answer.

FILE: inc\checks\class-check.php
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FOUND 0 ERRORS AND 3 WARNINGS AFFECTING 3 LINES
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 14 | WARNING | Property name "$_when" should not be prefixed with an underscore to
    |         | indicate visibility (PSR2.Classes.PropertyDeclaration.Underscore)
 23 | WARNING | Property name "$_status" should not be prefixed with an underscore to
    |         | indicate visibility (PSR2.Classes.PropertyDeclaration.Underscore)
 30 | WARNING | Property name "$_message" should not be prefixed with an underscore to
    |         | indicate visibility (PSR2.Classes.PropertyDeclaration.Underscore)
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FILE: inc\checks\class-file-contents.php
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FOUND 0 ERRORS AND 2 WARNINGS AFFECTING 2 LINES
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 34 | WARNING | Found: ==. Use strict comparisons (=== or !==).
    |         | (WordPress.PHP.StrictComparisons.LooseComparison)
 49 | WARNING | Found: ==. Use strict comparisons (=== or !==).
    |         | (WordPress.PHP.StrictComparisons.LooseComparison)
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FILE: inc\checks\class-file.php
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FOUND 0 ERRORS AND 2 WARNINGS AFFECTING 2 LINES
------------------------------------------------------------------------------------------
 15 | WARNING | Property name "$_when" should not be prefixed with an underscore to
    |         | indicate visibility (PSR2.Classes.PropertyDeclaration.Underscore)
 47 | WARNING | Property name "$_matches" should not be prefixed with an underscore to
    |         | indicate visibility (PSR2.Classes.PropertyDeclaration.Underscore)
------------------------------------------------------------------------------------------


FILE: inc\checks\class-option-value.php
------------------------------------------------------------------------------------------
FOUND 0 ERRORS AND 2 WARNINGS AFFECTING 2 LINES
------------------------------------------------------------------------------------------
 44 | WARNING | Found: ==. Use strict comparisons (=== or !==).
    |         | (WordPress.PHP.StrictComparisons.LooseComparison)
 52 | WARNING | Found: ==. Use strict comparisons (=== or !==).
    |         | (WordPress.PHP.StrictComparisons.LooseComparison)
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