[EFL][WK2] Relevant test classes should be redefined by inheriting from EWK2UnitTestBase as per each test file

[Donggwan Kim]

All the test files use EWK2UnitTestBase only.
There are many methods and variables defined in each test file as static.
It should be defined as relevant test class specific to each test file for more readability like below.

class EWK2FooTest : public EWK2UnitTestBase {
public:
    void foo();
};

[Donggwan Kim]

I uploaded the patch as sample. (https://bugs.webkit.org/show_bug.cgi?id=118717)
If this approach is accepted by a reviewer, i will modify all other test cases as well.

[Donggwan Kim]

All the dependent patches was fixed and closed.