Fix error messages not being displayed with nested input elements

[ndm2]

So it's been some time, but there hasn't really been any feedback on how to handle it.

The source of the problem is that the error message element is not a sibling of an (input) element with an is-invalid class. This PR fixes that problem in 3 different places, where the input element is nested in a div:

1. In input groups
2. In horizontally aligned checkboxes
3. In custom file controls

For input groups, Bootstrap now officially suggests to put the validation response as a sibling to an input group with an is-invalid class, so I thought it's safe to go that route, and add the error class to the input group wrapper. Before/After:

In horizontally aligned checkboxes, the message (and help text) is moved into the nesting div, which markup wise and visually will unify with default aligned checkboxes. Before/After:

For custom file controls I've chosen adding the error class to the wrapper div too, just like for input groups, because a) moving the message element into the wrapper requires some bigger changes with additional templates, and b) it produces a visual glitch as Bootstrap by default restricts the elements height, causing the error message to "overlfow" and being placed over other elements. Before/After:

Problem with message in the wrapper:

A word of warning, none of these fixes are compatible with custom client-side validation, but it didn't work before either, so there's that.

ps. The tests keep growing and growing, and I think I could combine the tooltip and error tests, and also throw in help text usage, that would reduce the clutter a bit, but I'd do that in a followup, I need some rest first, putting these tests together is really tedious.

/cc @ravage84 Not sure, but IIRC you wanted to be notified about this.

[codecov]

Codecov Report

Merging #314 into cake-4-bs-4 will increase coverage by 0.10%.
The diff coverage is 100.00%.

@@                Coverage Diff                @@
##             cake-4-bs-4     #314      +/-   ##
=================================================
+ Coverage          89.46%   89.56%   +0.10%     
- Complexity           272      277       +5     
=================================================
  Files                 19       19              
  Lines                816      824       +8     
=================================================
+ Hits                 730      738       +8     
  Misses                86       86              

Impacted Files	Coverage Δ	Complexity Δ
src/View/Helper/FormHelper.php	98.96% <100.00%> (+0.01%)	96.00 <0.00> (+3.00)
src/View/Widget/InputgroupTrait.php	96.61% <100.00%> (+0.24%)	19.00 <0.00> (+2.00)

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[ravage84]

@D4rkMindz please have a look and give feedback if you have any issues.