Support line continuation

[luis-j-soares]

A future OS release will introduce automatic line continuation in BrightScript, allowing expressions and function call arguments to span multiple lines after binary operators (+, -, *, /, \, mod, ^, and, or, and relational operators).

For BrighterScript users, this PR adds parser support for that syntax in BrighterScript mode without introducing a separate feature flag.

Standard .brs behaviour remains unchanged unless allowBrighterScriptInBrightScript is already enabled, and transpiled output is still normalized back to ordinary single-line BrightScript.

Behaviour

• Enabled in .bs files (BrighterScript mode)
• Enabled in .brs files only when allowBrighterScriptInBrightScript is set, because those files are then parsed in BrighterScript mode
• Standard .brs files still emit syntax errors for binary-operator continuation and multi-line call arguments
• Continued expressions and continued call arguments transpile back to single-line BrightScript output
• Existing multi-line collection literals used as call arguments remain supported in standard .brs

Coverage

• precise negative tests for standard .brs syntax errors
• transpile tests proving continued binary expressions and continued call arguments flatten back to one line
• regression tests proving multi-line array and associative-array literals as call arguments are still valid in standard .brs

Examples

Arithmetic operators

result = value1 +
         value2 *
         value3

ratio = totalWidth -
        padding /
        columns

Boolean operators

condition = isValid and
            isEnabled or
            isRequired

Relational operators

isInRange = x >=
            minValue and
            x <=
            maxValue

Chained across multiple lines

total = basePrice +
        tax +
        shippingCost -
        discount

Function call arguments split across lines

result = calculateValue(
    param1,
    param2
)

Inline collections as arguments (supported since BrightScript's inception — unaffected by this change)

foo({
    option1: true,
    option2: false
})

foo([
    1,
    2
])

[markwpearce]

Will we need to update the formatter as well?

[luis-j-soares]

Will we need to update the formatter as well?

@markwpearce I would say so. I can open an issue and work on it once this PR is merged.