Improve pluralization of terms for summaries in the product

[AR-May]

In every case when we say warning(s) or error(s) we know if the quantity is plural or not, so we should just pluralize the noun correctly - both on this final-build summary and on the per-project summaries.

See discussion in the PR.

In short, the current RESX-based localization method makes it very hard to report pluralized and singular terms for values without a large amount of developer overhead. This desired error report summary is one example, and in #9929 @nohwnd and I were discussing the same problem - reporting singular and plural forms of successes, failures, and skipped tests leads to an explosion of terms in order to support different language grammars and layout.

We need a system that doesn't impose so much burden on developers.

[nohwnd]

As an example a simple summary of a test run:

In english we need 2 variations:

Ran 0 tests
Ran 1 test

In czech we need 3 variations.

Spuštěno 0 testů
Spuštěn 1 test
Spuštěny 2 testy