We were getting a lot of warnings due to nested `find_package` calls
within `Find***.cmake` files. The recommended approach is to use
[`find_dependency`](https://cmake.org/cmake/help/latest/module/CMakeFindDependencyMacro.html)
in package configuration files. I made this change for all instances.
Case mismatches between `Find<Package>.cmake` and calling
`find_package(<PACKAGE>`) also lead to warnings. Fixed for
`FindPASTIX.cmake` and `FindSCOTCH.cmake`.
`FindBLASEXT.cmake` was broken due to calling `find_package_handle_standard_args(BLAS ...)`.
The package name must match, otherwise the `find_package(BLASEXT)` falsely thinks
the package wasn't found. I changed to `BLASEXT`, but then also copied that value
to `BLAS_FOUND` for compatibility.
`FindPastix.cmake` had a typo that incorrectly added `PTSCOTCH` when looking for
the `SCOTCH` component.
`FindPTSCOTCH` incorrectly added `***-NOTFOUND` to include/library lists,
corrupting them. This led to cmake errors down-the-line.
Fixes#2288.
(cherry picked from commit 1cdec386530c6b844389b96c199e723a1e4e71c7)
Ancient versions of CMake required else(), endif(), and similar block
termination commands to have arguments matching the command starting the block.
This is no longer the preferred style.
