Add ability to specify additional style preprocessor options

[StevenBarnettST]

Bug Report or Feature Request (mark with an x)

- [ ] bug report -> please search issues before submitting
- [x] feature request

Versions.

@angular/cli: 1.4.0
node: 8.4.0
os: win32 x64
@angular/animations: 5.0.0-beta.6
@angular/cdk: 2.0.0-beta.10
@angular/common: 5.0.0-beta.6
@angular/compiler: 5.0.0-beta.6
@angular/core: 5.0.0-beta.6
@angular/forms: 5.0.0-beta.6
@angular/http: 5.0.0-beta.6
@angular/material: 2.0.0-beta.10
@angular/platform-browser: 5.0.0-beta.6
@angular/platform-browser-dynamic: 5.0.0-beta.6
@angular/router: 5.0.0-beta.6
@angular/cli: 1.4.0
@angular/compiler-cli: 5.0.0-beta.6
@angular/language-service: 5.0.0-beta.6
typescript: 2.5.2

Desired functionality.

Please add the ability to specify additional style preprocessor options to be used during compile.

Specifically, I want to be able to enable strict math (strictMath: true) for the Less preprocessor.

Mention any other details that might be useful.

This option is enabled by adding an additional property to the less-loader options, like the second example in the less-loader readme:

            loader: "less-loader", options: {
                strictMath: true,
                noIeCompat: true
            }

The stylePreprocessorOptions setting in the config schema sounds like a great place to add configuration for this. The options already being configured could be merged with any specified in that config object.

[StevenBarnettST]

@AhsanAyaz this is a different issue than the other ones addressed by #7648.

[AhsanAyaz]

@StevenBarnettST you're right. I removed it from the comment there.

[clydin]

An argument could be made to always enabled the strictMath option. There's really no need to optimize any math expressions in a dev mode. In production, cssnano should already handle this category of optimization.

[StevenBarnettST]

@clydin While personally I'd be fine with having strictMath always enabled, it would be a breaking change for people with code that assumes it is disabled. In addition, the Less documentation says they "originally planned to default this to true in the future, but it has been a controversial option".