validate compiler options in multicompiler mode

[vankop]

What kind of change does this PR introduce?
feature
closes #14843

Did you add tests for your changes?
yes

Does this PR introduce a breaking change?
no

What needs to be documented once your changes are merged?
nothing

[webpack-bot]

For maintainers only:

• This needs to be documented (issue in webpack/webpack.js.org will be filed when merged)
• This needs to be backported to webpack 4 (issue will be created when merged)

[vankop]

@alexander-akait what do you think about this PR? should we somehow define unique name in this case?

[alexander-akait]

@vankop I think validation of the uniqueName make sense too, because using the same can be problems too, for better dx let's generate a new unique name (just add a number based on index if multicompiler array) and output a warning

[vankop]

@alexander-akait fixed. As I understand cache does not work correctly with same name, so name always should be unique

[vankop]

fixed @alexander-akait

[alexander-akait]

Let's add a test where we have two true values and so don't have any problems

[alexander-akait]

@vankop I made some improvements of your idea

• avoid extra loops (better perf), we already apply webpack default options, so for multi compiler mode we can just pass index of compiler and make default name using this index
• by default we use name and mode for cache names, so let's respect if for multi compiler mode (i.e. when both configuration doesn't have name, we use name + mode + compiler_index)
• now we output the warning if you have name: "default" for both compilers (test cases added)
• if you have node API for webpack you don't need to apply new default, we will do it under the hood (better DX)

[alexander-akait]

Also always output warnings when you explicitly set the same cache names

[alexander-akait]

Feel free to merge and merge if it is ok

[alexander-akait]

We need fix our tests and do not run cache test for basic test, I will tr to fix it tomorrow or you can do it, thank you

[webpack-bot]

@vankop Thanks for your update.

I labeled the Pull Request so reviewers will review it again.

@alexander-akait Please review the new changes.