feat(linter/plugins): implement SourceCode#getIndexFromLoc method

[overlookmotel]

WIP. Need to add tests and refactor.

Implement sourceCode.getIndexFromLoc API, using the lines array added in #14290.

[overlookmotel]

• feat(linter/plugins): implement SourceCode#getIndexFromLoc method #14295 👈 (View in Graphite)
• main

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[Copilot]

Pull Request Overview

This PR implements the sourceCode.getIndexFromLoc method that converts line/column positions to character indices in the source text. The implementation uses the lines array infrastructure added in a previous PR.

• Implements complete getIndexFromLoc method with input validation and edge case handling
• Optimizes initLines function by adding early return guard to prevent redundant initialization
• Replaces explicit length check with direct initLines() call in lines getter

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[Copilot]

Missing null check for sourceText. The code calls initLines() which may call initSourceText(), but there's no guarantee that sourceText is not null at this point. Add a null check or ensure sourceText is properly initialized.

Suggested change

	if (line === linesCount) {
	if (line === linesCount) {
	if (sourceText == null) {
	throw new TypeError("sourceText is null or undefined when accessing its length.");
	}

[Copilot]

Potential array bounds error. The code accesses lineStartOffsets[line] where line could equal linesCount, but lineStartOffsets may only have linesCount elements (0-indexed). This could cause an out-of-bounds access when line === linesCount.

Suggested change

	} else {
	} else {
	// line is guaranteed to be < linesCount here, so lineStartOffsets[line] is in bounds
	console.assert(line < linesCount, "lineStartOffsets[line] out of bounds");

[overlookmotel]

Superceded by #14303.