Replace __call__() by _element_constructor_() in MatrixSpace

[pjbruin]

The MatrixSpace class still has a __call__() method instead of _element_constructor_(). This is relatively easy to change, and has the benefit that if M is a matrix space and m an element of M, then M(m) simply returns m. This can be viewed as a small addendum to #23719.

One side effect of the attached branch is that the first argument (entries) is now effectively a mandatory non-keyword argument, and copy and coerce are keyword-only arguments. This is probably a good thing for readability, though.

Depends on #31072

Component: coercion

Author: Peter Bruin

Branch/Commit: c9f048b

Reviewer: David Roe

Issue created by migration from https://trac.sagemath.org/ticket/31078

[pjbruin]

Branch: u/pbruin/31078-MatrixSpace_element_constructor

[pjbruin]

Commit: cef613a

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

0b666b4

Trac 31078: small simplification

[sagetrac-git]

Changed commit from cef613a to 0b666b4

[mkoeppe]

comment:3

Setting new milestone based on a cursory review of ticket status, priority, and last modification date.

[roed314]

Reviewer: David Roe

[roed314]

comment:4

Looks good to me. Most recent test failure is spurious.