This patch adds semantics for the `omp fuse` directive in flang, as
specified in OpenMP 6.0. This patch also enables semantic support for
loop sequences which are needed for the fuse directive along with
semantics for the `looprange` clause. These changes are only semantic.
Relevant tests have been added , and previous behavior is retained with
no changes.

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Co-authored-by: Ferran Toda <ferran.todacasaban@bsc.es>
Co-authored-by: Krzysztof Parzyszek <Krzysztof.Parzyszek@amd.com>

OpenMP 6.0 introduced a `fuse` directive, and with it a "loop sequence"
as the associated code. What used to be "loop association" has become
"loop-nest association".

Rename Association::Loop to LoopNest, add Association::LoopSeq to
represent the "loop sequence" association.

Change the association of fuse from "block" to "loop sequence".

This PR fixes a Fortran syntax violation in the OpenMP default mapper
naming convention. The suffix .omp.default.mapper contains dots which
are invalid in Fortran identifiers, causing failures when mappers are
written to and read from module files. The fix changes the suffix to
_omp_default_mapper which uses underscores instead of dots, complying
with Fortran syntax rules.

Key changes:

- Changed OmpDefaultMapperName constant from .omp.default.mapper to
_omp_default_mapper
- Added GetUltimate() calls in mapper symbol resolution to properly
handle symbols across module boundaries
- Added new test case verifying default mappers work correctly when
defined in a module and used in consuming programs

This fixes #168336.

Instead of storing a variant with specific types, store parser::Block as
the body. Add two access functions to make the traversal of the nest
simpler.

This will allow storing loop-nest sequences in the future.

This patch adds support to emit default declare mappers for implicit
mapping of derived types when not supplied by user. This especially
helps tackle mapping of allocatables of derived types.

Reverts llvm/llvm-project#163860

- Implemented semantic TODO to catch undeclared mappers.
- Fix mapper lookup to include modules imported through USE.
- Update and add tests.

Fixes #163385.

Support for lowering collapse already exists within
`genLoopNestClauses`, which is called when lowering taskloop. However,
the TODO message still included the Collapse clause, so it was not
activated. By removing this, it enables lowering of the Collapse clause
in taskloop.

This patch add MLIR lowering support for nogroup, reduction, inreduction
and lastprivate clauses of taskloop directive.