Revert the router's path string decoding strategy (fixes #3064)

[kfule]

Description

This PR reverts the router’s initial decoding strategy during route path resolution to behavior similar to v2.3.7 and earlier.

#3050 fixed a decoder bug. However, because the decoder is now applied more aggressively than before, it appears to have had an unintended effect on path-segment parsing.

Additionally, since decodeURIComponent was being used directly within compileTemplate(), this PR changed it to use decodeURIComponentSafe instead.

Motivation and Context

fixes #3064

How Has This Been Tested?

npm run test
Additionally, I confirmed improved behavior in the following flems.

// fallback
const def = {view: () => "default"}

const abc = {
  view: ({attrs}) => [
    m("div", "a: " + attrs.a),
    m("div", "b: " + attrs.b),
    m("div", "c: " + attrs.c)
  ]
}

m.route(document.body, "/", {
  "/": def,
  "/a/:a/b/:b/:c...": abc
})

// m.route.set("/a/foo/b/bar/baz")
m.route.set("/a/fo%3Fo/b/bar/baz") // ?
// m.route.set("/a/fo%23o/b/bar/baz") // #
// m.route.set("/a/fo%2Fo/b/bar/baz") // /
// m.route.set("/a/fo%E0%80%80o/b/bar/baz") // malformed URI sequence

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• I have added tests to cover my changes.
• All new and existing tests passed.
• My change requires a documentation update, and I've opened a pull request to update it already:
• I have read https://mithril.js.org/contributing.html.