Track file dependencies for global constant fetches

[SanderMuller]

DependencyResolver recorded file dependencies for class constants, functions, methods and properties, but not for global/namespaced constant fetches (Node\Expr\ConstFetch). On top of that, global constant declarations were not exported nodes. The result cache re-analyses a changed file's dependents only when the changed file's exported nodes change, so a file that reads a global constant was never re-analysed when that constant changed, leaving a stale result.

This fixes both halves:

1. Record a dependency on the file declaring a fetched global constant (ConstFetch in DependencyResolver), guarding the ubiquitous true/false/null literals so the common path stays a couple of string comparisons.
2. Export global constant declarations (name + value) as RootExportedNodes, like class constants already are, so renaming or changing a constant re-analyses the files that use it.

Two ways to hit the stale result, both fixed and covered by the result-cache-constants e2e test:

• editing a global constant's declaration; the files reading it are re-analysed on the next run;
• bumping a Composer package that declares the constant; with package-granular cache invalidation the reading file is now among the re-seeded files.

Performance

The ConstFetch branch runs for every constant fetch, so it is guarded. Measured over a cold, single-process analysis:

corpus	level	ConstFetch nodes	skipped (true/false/null)	getConstant() calls	added time
phpstan-src	8	10,151	9,928	223	4.9 ms
a doctrine/symfony app	5	12,279	11,348	930	16.5 ms
laravel/laravel	5	8,151	7,676	474	9.6 ms

Added time is under 0.02% of analysis CPU, and that figure is an upper bound (it includes the measurement probes). The exported-node part runs only for global const declarations, which are rare.

Reproducing the staleness

// a.php
<?php declare(strict_types = 1);
namespace App;
const MODE = 1;

// b.php
<?php declare(strict_types = 1);
namespace App;
function f(): int { return MODE; }

vendor/bin/phpstan analyse a.php b.php   # no errors; cache warm
# change a.php to: const MODE = 'x';
vendor/bin/phpstan analyse a.php b.php   # before: stale, still no error

Before this change the second run keeps b.php cached and reports nothing; a cold run reports that f() returns string. With the change the second run re-analyses b.php and matches the cold run.

[phpstan-bot]

This pull request has been marked as ready for review.