Enable UglifyJS compatibility workarounds

[colinrotherham]

This PR lowers the threshold for function calls being "inlined" in UglifyJS to fix:

• Minified JS in dist errors in IE8 #3136

Running our minified bundle in IE8 sees the Event polyfill fail to patch Element.prototype.addEventListener due to polyfill code being "inlined" with unexpected side effects.

Various unpublished inline improvements been made since the last uglify-js@3.17.4 release:

• fix corner case in inline & unused mishoo/UglifyJS#5725
• fix corner case in inline mishoo/UglifyJS#5736
• fix corner case in inline mishoo/UglifyJS#5742
• fix corner case in inline mishoo/UglifyJS#5760
• fix corner case in functions & inline mishoo/UglifyJS#5767

These might fix it, but for now we can disable inlining functions with variables and statements

Before

compress: {
  inline: true // inline functions with arguments, variables and statements
}

After

compress: {
  inline: 2 // inline functions with arguments
}

Also included are various flags to opt out of optimisations that can break older browsers

module: false,
v8: true,
webkit: true

UglifyJS compress options

https://github.com/mishoo/UglifyJS#compress-options

inline (default: true) — inline calls to function with simple/return statement:

false — same as 0
0 — disabled inlining
1 — inline simple functions
2 — inline functions with arguments
3 — inline functions with arguments and variables
4 — inline functions with arguments, variables and statements
true — same as 4

[colinrotherham]

Whilst it turned out not to be related, I've also added a missing Event polyfill to Accordion

Moved to:

• Add missing Event polyfill to accordion component JavaScript #3150

[colinrotherham]

@36degrees I'm going to merge this in as initial testing looks good

Won't focus on it as we're nearly set to replace it with Terser once testing is complete:

• Swap JavaScript minifier from UglifyJS to terser #3013