JIT: Change IntegralRange to handle arbitrary int64_t

[BoyBaykiller]

Comment on IntegralRange says:

runtime/src/coreclr/jit/compiler.h

Lines 1189 to 1191 in b745957

	// Represents an integral range useful for reasoning about integral casts.
	// It uses a symbolic representation for lower and upper bounds so
	// that it can efficiently handle integers of all sizes on all hosts.

Yet when I change it to use plain int64_t the tp diffs are negligible.

This change will allows us to tighten ranges and potentially enable some optimizations.
The very reason I did this is to be able to handle #126529 (comment)
And just overall its the more natural thing.

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