Feat: Dynamic import refinements & fixes, optimization

[guybedford]

This PR upgrades dynamic import analysis, as described in the readme diff here, and fixes #56, #53 and #98.

To summarize the changes:

• d no longer tracks the start of the dynamic import statement import('x') but rather the start of the bracket at ('x')
• The ss to se range can be reliably used for the whole statement import('x')
• The s and e range will either be the inside of the brackets for an unknown expression, or the exact quoted string start and end position after whitespace and comments but including the quotes for a string literal import.

This also includes a bugfix for the asm.js build with multiline dynamic imports.

Since this is a breaking change it will be the 0.10 release.

It also includes some hard-won optimization work bringing the footprints from:

    dist/lexer.js:  4,670B Brotli (11,532B raw)
dist/lexer.asm.js:  4,975B Brotli (19,476B raw)

to:

    dist/lexer.js:  4,512B Brotli (10,668B raw)
dist/lexer.asm.js:  4,685B Brotli (16,896B raw)