Fixes for bugs in fgMorphCast and optNarrowTree. (dotnet/coreclr#18816)

Fixes for bugs in fgMorphCast and optNarrowTree. (dotnet/coreclr#18816)

The fix under NARROW_IND prevents transformation of, e.g.,
CAST      int <- ushort <- int
    CLS_VAR byte

into

CLS_VAR byte.

With the fix the CAST is not removed.

The fix under GT_CAST prevents transformation of, e.g.,

CAST      int <- ushort <- long
    CAST      long <- int
       expr short

into

expt short.

With the fix it gets transformed into

CAST      int <- ushort <- int
    expr short

Block cast optimizations in fgMorphCast if the cast expression is an
active CSE candidate.

Update cast expression value numbers when a cast is removed.

Fixes dotnet/coreclr#18238, dotnet/coreclr#18850.

No diffs in frameworks and tests (pmi and crossgen, x64 and x86), except for the added test cases.

Commit migrated from https://github.com/dotnet/coreclr/commit/4929ebab22bcef4f6ff39acbcdb333ffeb98f24a