[Bug]: FieldsAre cannot support struct type

### Describe the issue

the documentation about FieldsAre wrote:
```cpp
struct MyStruct {
int value = 42;
std::string greeting = "aloha";
};
MyStruct s;
EXPECT_THAT(s, FieldsAre(42, "aloha"));
```
however, when I run this:
```cpp
struct MyStruct {
int value = 42;
std::string greeting = "aloha";
};
TEST(MyTestSuite, FieldsAreMatcherTest) {
MyStruct s;
EXPECT_THAT(s, FieldsAre(42, "aloha"));
}
```
g++ cannot compile:
note: types 'std::pair<_Tp1, _Tp2>' and 'const MyStruct' have incompatible cv-qualifiers

### Steps to reproduce the problem

wrote the above code and run googletest

### What version of GoogleTest are you using?

1.15.2

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

windows10

### What compiler and version are you using?

gcc (tdm64-1) 9.2.0

### What build system are you using?

cmake version 3.22.2

### Additional context

_No response_

Start with the FieldsAre documentation example and reproduce the reported compilation failure using the supplied MyStruct code, GoogleTest 1.15.2, and g++ 9.2.0. Trace the matcher behavior involved in the incompatible std::pair and MyStruct types. Done means the documented struct example compiles and the corresponding matcher test passes.

Written by the indexing model from the issue text.