[ty] remove `static_expression_truthiness` and improve reachability analysis (#22971)
## Summary
cf: https://github.com/astral-sh/ruff/pull/19579,
https://github.com/astral-sh/ruff/pull/20566#discussion_r2553196955
Currently, we use the query `static_expression_truthiness` to determine
the truthiness of an expression.
This always determines the truthinesses of non-definitely-bound places
as `Ambiguous`, preventing cycles that occur when their reachabilities
depend on themselves. However, this can lead to inaccurate analysis of
code like the following.
```python
def _(flag: bool):
if flag:
ALWAYS_TRUE_IF_BOUND = True
# error: [possibly-unresolved-reference] "Name `ALWAYS_TRUE_IF_BOUND` used when possibly not defined"
if ALWAYS_TRUE_IF_BOUND:
x = 1
else:
x = 2
# If `ALWAYS_TRUE_IF_BOUND` were not defined, an error would occur, and therefore the `x = 2` branch would never be executed.
reveal_type(x) # expected: Literal[1], but: Literal[1, 2]
```
Since #20566, we can determine the `Place` by looking at the previous
cycle result.
Therefore, we can now remove `static_expression_truthiness`, improving
reachability analysis of the above code.
## Test Plan
mdtest updated
ruff
48a4d9d7 - [ty] remove `static_expression_truthiness` and improve reachability analysis (#22971)
