Documentation: replace type with struct and/or mutable struct

[fsaad]

There are a few places in the stable documentation that mention the type keyword (which is gone, #19157), e.g. the phrases "type block" and "type definition block" should be changed to mention struct or mutable struct.

Here are a few of the offending instances that I found in doc/:

/tmp/julia $ git grep '`type`' doc | grep \.md
doc/src/manual/calling-c-and-fortran-code.md:variables will not be visible in Julia unless the type is mutable (declared via `type`). However,
doc/src/manual/constructors.md:`type` block.
doc/src/manual/constructors.md:constructor only for `SummedArray`, but inside the `type` definition block to suppress
doc/src/manual/faq.md:This does not apply to `function` or `type` declarations. However, anonymous functions bound to global
doc/src/manual/noteworthy-differences.md:  * Julia's `type`s do not support dynamically adding fields at runtime, unlike MATLAB's `class`es.

[JeffBezanson]

Great catch, thank you.