Allow getting type from template declarations.

[skl131313]

struct TypeObj
{
    alias This = typeof(this);

    mixin template MixinTempl()
    {
        int value;
    }
}

ref TypeObj Obj()
{
    static TypeObj a;
    return a;
}

void main()
{
    mixin Obj.This.MixinTempl; // ok
    mixin Obj.MixinTempl;      // error: "MixinTempl!()" is not defined
}

Couldn't access templates like in the above example, though other symbols such as types are accessible. This allows the second line to be usable.

[dlang-bot]

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	18591	enhancement	DMD should allow access to mixin template declarations

[wilzbach]

edit: covered now. Thanks!

[WalterBright]

Thanks for your contribution. This needs an issue raised in Bugzilla which this PR can then resolve.

[wilzbach]

In the interest of moving quickly, I created a Bugzilla issue, referenced it in the commit message and squashed your commits.