Require 99 % type coverage

[TomasVotruba]

Follow-up to #8221, which brought in tomasvotruba/type-coverage.

Turns on the type_coverage thresholds that ship with it:

+    # see https://github.com/TomasVotruba/type-coverage
+    type_coverage:
+        declare: 99
+        return_type: 99
+        param_type: 99
+        property_type: 99
+        constant_type: 99

PHPStan then fails if any of these drop below 99 %:

Class constant type coverage is 98.0 % out of 738 possible
    Add more class constant types to reach 99 % coverage

Current numbers, measured with type_coverage: measure: true:

metric	coverage	of
Class constant type	99.7 %	738
Param type	99.9 %	7772
Property type	100.0 %	360
Return type	99.9 %	7449
Strict declares	99.9 %	2766

So this is a floor, not a task list - nothing to fix right now, it only stops the numbers from sliding.