Let final and abstract be used as variable names

[ghedwards]

Closes #46.

Every other modifier keyword already worked as an ordinary name — public, private, package, remote, component, interface, static — because the identifier rule lists them. FINAL and ABSTRACT were missing:

final = 3;      // no viable alternative
abstract = 4;   // no viable alternative

Same shape as the three recorded in CLAUDE.md, and the same fix: add them to identifier alongside default, var, to, include, new.

The part worth reviewing

FINAL now serves double duty. final x = 1; is Lucee's immutable local, added in #34, so the token both starts a declaration and is a name. A green parse proves nothing here — the question is whether the two still build different trees:

input	decompiles as	meaning
final = 3;	final = 3	assignment to a variable called final
final x = 1;	final x = 1	immutable local declaration
var final = 1;	var final = 1	local declaration of a variable called final
final var y = 2;	final y = 2	immutable local

All four distinct, and the fixture pins them together so a later change can't quietly collapse one into another. The modifier positions (abstract component {}, final function f() {}) are unaffected.

One cosmetic note: final var y = 2 decompiles as final y = 2, dropping the var. Both spell the same thing and CFVarDeclExpression carries a single flag rather than tracking both keywords — pre-existing from #34, not introduced here.

Verification

• 313 cfparser tests, ./gradlew build
• Differential harness 8 → 6 — both corpus cases that cover this (identifier-capable keywords still work as identifiers and keywords as variable names), nothing newly broken
• CFLint 675 against a clean build
• Fixture fails with cfml.parsing/src/main stashed

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