fix(alphatex): accept fractional harmonic values

[Danielku15]

Note

AI-authored disclosure (alphatab-ai-authored-v1)

Portions of this content were authored by an AI agent. The agent has read
AGENTS.md and the human submitter accepts responsibility for
compliance with the rules in that document.

Issues

Fixes #2896

Proposed changes

#2896: the alphaTex exporter writes fractional harmonic values as they are, e.g. {ah 2.4}, but the importer rejects that output with AT206/AT202. Guitar Pro uses such values (2.4, 2.7, 3.5, 8.5, …), so these scores cannot be loaded again after an export.

The alphaTex lexer reads 2.4 as 2, ., 4, because <fret>.<string> depends on that. An argument is only read as a float where its parameter is declared as one (RequiredAsFloat/OptionalAsFloat). The value parameter of ah, th, ph, sh and fh was declared as a plain Optional (integer). The importer therefore read 2, and the . that followed broke the property group.

The fix declares that parameter as OptionalAsFloat, as fermata length already does, and regenerates AlphaTex1LanguageDefinitions.ts. The lexer, parser, importer and exporter are unchanged.

Input	Before	After
3.3{ah 2.4} (same for th, ph, sh, fh)	AT206 + AT202	harmonicValue = 2.4
3.3{ah 7}	7	7 (unchanged)
3.3{ah}	unchanged	unchanged
Export → import with harmonicValue = 2.4	fails	round-trips

Tests

• AlphaTexImporter.test.ts: new harmonic-values-fractional test. It imports one fractional value for each of the five harmonic types and checks type and value, then exports and re-imports. It fails before the fix with the errors from the issue.

The TypeScript, C# and Kotlin builds and test suites pass.

Checklist

• I consent that this change becomes part of alphaTab under its current or any future open source license
• This PR is linked to an accepted issue (see above)
• Changes are implemented
• New tests were added
• I have read AGENTS.md if an AI helped draft any part of this PR

AI authorship disclosure

• No AI agent authored any part of this PR (description, code, tests, or commit messages)
• An AI agent contributed to this PR. The AI-authored disclosure block
  (alphatab-ai-authored-v1) is present at the top of this body, and I have
  personally reviewed every change and can explain each one

Further details

• This is a breaking change
• This change will require update of the documentation/website