Fix static extents assignment for LayoutLeft/LayoutRight assignment

[crtrott]

We always supported the following:

Kokkos::View<int[5]> a("A");
Kokkos::View<int[5]> b("A");
Kokkos::View<int*> c("C",5);
a = b;
b = a;
b = c;

We also supported for always:

Kokkos::View<int*,Kokkos::LayoutLeft> a("A",5);
Kokkos::View<int*,Kokkos::LayoutRight> b("B",5);
a = b;
b = a;

What apparently doesn't work is:

Kokkos::View<int[5],Kokkos::LayoutLeft> a("A");
Kokkos::View<int[5],Kokkos::LayoutRight> b("B");
a = b;
b = a;

Turns out we do some extra checks for dynamic rank match, when accounting for LayoutLeft/LayoutRight convertibility of Rank 0 and Rank 1 Views.
That check is unnecessary, since it will get checked via the dimension assignability check already.
I.e. we hadn't properly orthogonalized the extents assignability from the Layout assignability for mixing LayoutLeft/LayoutRight.

This fixes this by getting rid of the erroneous condition.

[crtrott]

Note the proper dimension check happens around line 281 or so.

[crtrott]

Fixes #5534 @lucbv

[crtrott]

That line 1133 is the offending check.

[crtrott]

Note this behavior was always intended (as the fact that it works for matching layouts attest too) and this is also how mdspan works.

[lucbv]

I talked this through with @crtrott and agree with the logic

[dalg24]

The view assignable unit test could use some refactor (not requesting changes just saying)
Your changes should enable rank-0 view assignments as well isn't it? If I am not mistake please add tests for it.

[dalg24]

Wait why do you pass 5? Isn't it something we only relaxed not so long ago? kokkos/kokkos-core-wiki#108
Please drop it here and below.

[crtrott]

yeah unnescessary here, gonna change that.

[crtrott]

Also added the rank-0 mixed layout case.

[dalg24]

No right -> left?

[crtrott]

I guess we could add them everywhere, but mostly this is about mismatch, not any specific layouts.