[Documentation]: Clarify which string comparison macros support wide strings

### Describe the issue

## Summary

There seems to be an inconsistency in the documentation regarding wide string (`wchar_t*`) support in string comparison assertions.

## Details

In older versions of the documentation (e.g. v1.10.x), the [primer.md](https://github.com/google/googletest/blob/v1.10.x/googletest/docs/primer.md#string-comparison) stated:

> `*STREQ* and *STRNE* also accept wide C strings (wchar_t*).`

In newer versions (e.g. v1.12.x and later), this wording in [reference/assertions.md](https://github.com/google/googletest/blob/v1.12.x/docs/reference/assertions.md#string-comparison-c-strings) changed to:

> `These assertions also accept wide C strings (wchar_t*).`

This phrasing makes it look like all string-related assertions (including `EXPECT_STRCASEEQ` / `EXPECT_STRCASENE`) support wide C strings.
However, based on the implementation and testing, only `EXPECT_STREQ` and `EXPECT_STRNE` actually support `wchar_t*`. The case-insensitive variants (`EXPECT_STRCASEEQ` / `EXPECT_STRCASENE`) do **not** support wide strings.

## Expected

The documentation should clearly state that **only** `EXPECT_STREQ` and `EXPECT_STRNE` support `wchar_t*`, and that the case-insensitive variants do not.

## Suggested fix

Reword the documentation to explicitly mention which macros support wide C strings, to avoid confusion for users.

Example:

> "`EXPECT_STREQ` and `EXPECT_STRNE` also accept wide C strings (`wchar_t*`).
> Case-insensitive variants (`EXPECT_STRCASEEQ` and `EXPECT_STRCASENE`) currently do not support wide C strings."

---

This should help clarify the intended behavior and avoid misleading readers.

### Steps to reproduce the problem

```c++
#include

#include

TEST(Tests, Test) {
EXPECT_STRCASEEQ(L"HELLO", L"hello"); // cannot compile
EXPECT_STRCASENE(L"HELLO", L"hello"); // cannot compile
}

int main(int argc, char **argv) {
::testing::InitGoogleTest(&argc, argv);
return RUN_ALL_TESTS();
}
```

### What version of GoogleTest are you using?

1.17.0

### What operating system and version are you using?

Windows 11 24H2

### What compiler and version are you using?

`cl.exe`
Microsoft (R) C/C++ Optimizing Compiler Version 19.44.35213 for x64

### What build system are you using?

`cmake --version`
cmake version 4.0.3

### Additional context

_No response_

Start with docs/reference/assertions.md at the string-comparison C-strings section, then compare its wording with the implementation and behavior described in the issue. Clarify that only EXPECT_STREQ and EXPECT_STRNE accept wchar_t*, while EXPECT_STRCASEEQ and EXPECT_STRCASENE do not; the documentation is done when it no longer implies otherwise.

Written by the indexing model from the issue text.