Revert "FIX: replace spurious 1.0E+12 by finfo(float).max in slsqp"

This reverts commit ccecd81bc4490b1cf71be85d31d838013d8fca7e.

Closes #3108.

(cherry picked from commit 1c04787ac5064421a61d5a042ce4916b28ace8ba)
DOC: Document how SLSP handles infinite values in bounds

(cherry picked from commit 03d2431c0c57fb4c446393ca5a19308d8dc1eca4)
TST: Add a test for SLSQP with bounds

(cherry picked from commit 6a0fa36ada20f5fe3d7295783f86cbb48f2e709c)