fix Issue 11505 - Bad error message: "opAssign [...] is annotated with @disable"
fix Issue 11554 - `is(T == enum);` produces an error if T is an enum defined with no members
fix Issue 7966 - First template instantiation inside `with` results in `Error 42: Symbol Undefined`

Always use `WithScopeSymbol` to make correct chain of `scopesym->parent`.
More better fix for issue 11376
fix Issue 11525 - Error: 'a[] *= a[]' each element is not a scalar, it is a Complex!double
fix Issue 11596 - Internal error: backend/cgcs.c 351
fix Issue 8117 - Cannot initialize struct member without default constructor
fix Issue 11479 - template members ignore private attribute in ddoc
vcbuild: make output of real nan/inf consistent with dmc compiled dmd
Codeview: map __vector(T) types to the static array T
Merge pull request #2898 from 9rnsr/fix11596

[REG2.065a] Issue 11596 - Internal error: backend/cgcs.c 351
Merge pull request #2899 from 9rnsr/fix8117

Issue 8117 - Cannot initialize struct member without default constructor
Merge pull request #2903 from rainers/issue10224

fix Issue 10224:  core.simd ICE cgcv.c line 2162 when compiling with -g
Merge pull request #2889 from 9rnsr/fix11554

[REG2.065a] Issue 11554 - `is(T == enum);` produces an error if T is an enum defined with no members
Merge pull request #2890 from 9rnsr/fix7966

Issue 7966 - First template instantiation inside `with` results in `Error 42: Symbol Undefined`
Merge pull request #2891 from 9rnsr/fix11525

[REG2.065a] Issue 11525 - Error: 'a[] *= a[]' each element is not a scalar, it is a Complex!double
fix Issue 11627 - [CTFE] cannot cast dchar to char at compile time on AA assignment
fix Issue 11614 - Error: this for _expand_field_0 needs to be type Tuple not type Foo

Even if a variable has no valid context, it would be either:

1. a part of compile time evaluated expression, which is used as unreal context.
    enum x = Type.fieldvar.sizeof;
    // It's legitimate expression so fieldvar is not evaluated
    // in runtime.

2. or an invalid field access without valid 'this', in runtime evaluated expression.
    int y = Type.fieldvar;
    // It's invalid expression so fieldvar access has no valid 'this'.

For the case #2, it will be an error by `checkRightThis` later. Therefore `getRightThis` should not make it an error.
Merge pull request #2804 from 9rnsr/fix11505

[REG2.064] Issue 11505 - Bad error message: "opAssign [...] is annotated with @disable"
Merge pull request #2897 from 9rnsr/fix11614

[REG2.064] Issue 11614 - Error: this for _expand_field_0 needs to be type Tuple not type Foo