feat: perch coverage mutates method calls, literals and chains like Stryker

[jbrown9513]

The mutant table stopped at operators, conditions, literals, statement calls and bodies: a method's own calls were never touched. items.filter(x => x.ok).map(…) got no mutant, so a test that never checks the filter was never found. Stryker mutates all of it.

src/mutants.js now makes the rest of Stryker's set, in every language perch reads:

Kind	Edit
method	A method becomes its opposite, or its call drops out of the chain, so the chain runs without it: startsWith to endsWith, toUpperCase to toLowerCase, min to max, every to some; .trim(), .filter(…), .sort(), .slice(…), .reverse() gone. Each language's own names: Python's strip and sorted(…), Ruby's upcase and select {…}, Kotlin's uppercase and sorted(), Swift's hasPrefix, Go's strings.ToUpper and strings.TrimSpace(…), Rust's to_uppercase and .rev(), C#'s Where(…) and OrderBy, Scala's forall and .sorted, PHP's strtoupper and array_filter(…), Lua's string.upper, C++'s std::min and std::any_of. Only a method that gives back its receiver's kind is dropped, so the edit compiles wherever the language checks types.
collection	A list, dictionary or object literal is emptied: [1, 2] to [], { a: 1 } to {}, {1} to set(), []int{1, 2} to []int{}, new int[]{1, 2} to new int[]{}, vec![1, 2] to vec![]. An empty list is filled, [] to ["perch was here"], where the language lets it stand alone. Kotlin's listOf() and Swift's [] have no type of their own and are left alone.
chaining	An optional chain is made unconditional: a?.b to a.b, a?.() to a(), Ruby's a&.b to a.b, PHP's ?-> to ->, Kotlin's ?. to !!., C#'s a?.b to a.b.
lambda	An arrow function's expression body returns undefined.
regex	A regular expression loses an anchor, a + becomes * and back, a ? goes, \d becomes \D, \w and \s likewise, [^a] becomes [a], each its own mutant. JavaScript and Ruby literals.
condition	Now also a ternary's condition, forced each way, and a for or do loop's, forced false.
update	Now every assignment operator Stryker turns: *= and /=, %= to *=, <<= and >>=, &= and |=, &&= and ||=, ??= to &&=, Python's //=.
logic	?? becomes &&, where && takes any value.
string	An empty string is filled: "" to "perch was here".

The mutants for a method call are read off each grammar's own shape: a member call in JavaScript, Python, Java, Go, Rust, C++, Lua and PHP; a navigation suffix in Kotlin and Swift; the receiver on the call itself in Ruby; a field access with no parentheses in Scala. A dropped call is described as the call to \trim` removed, and the test to add names it: Add a test that fails when `filter` is not called on line 12.`

On the shop fixture the count goes from 27 mutants to 28. On perch, 20,374 mutants become 32,822: 1,387 method swaps and drops, 2,249 collections, 2,011 arrow functions, 709 pattern edits, and the rest ternaries, loops and assignment operators; the score reads 27% where it read 28%.

Closes #349

[jbrown9513]

Stacked on #348, which is stacked on #345; merge those first, in that order.

[perchcode-bot]

Perch Scan: no issues in 40 methods at f765a28.

See the scan

[jbrown9513]

Folded into #355.