Compiler: Deduplicate conversion origins based on register's contentHEADdev

In the type propagator, when encountering back jumps, we need to run the
pass again in order to ensure that the state of the registers at the
target of the jump is fully known.

For this, we need to compare the latest state in the current pass with
states we have encountered earlier. If a match is found, no more passes
are needed.

The propagation is run multiple times and state is accumulated between
passes. For certain conversions, this will try to append types as
origins again every iteration. These would previously have been
deduplicated by QQmlJSTypeResolver::merge but, since the change at
1e095058e165b1c2f244799ca1928ae4cc046a2c, we consider 2 registers to be
equal only if their d pointers are equal. And since instructions such as
MoveRegexp create a new register for the literal type RegExpr every
time, the pointer doesn't match with the one from the register created
by the instruction during the ealier pass. This would lead to set of
origin types growing forever and to the state never matching a previous
one. This, in turn, caused an infinite loop because an additional pass
was always deemed necessary.

Therefore, restore the old logic that deduplicates based on contained
type, variant, and (recursively) scope.

Amends 1e095058e165b1c2f244799ca1928ae4cc046a2c

Fixes: QTBUG-135457
Pick-to: 6.9
Change-Id: I23167e95b958304698d12537598c1d72b03a5364
Reviewed-by: Ulf Hermann <[email protected]>
Reviewed-by: Olivier De Cannière <[email protected]>

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