SI-7618 Remove octal number literals

This also fixes a spurious detection of octal literals in floating
point literals: Literals like 01.23 are neither deprecated nor planned
for removal.
SI-8059 Override immutable.Queue#{+:,:+} for performance

Without those overrides, all elements are unnecessarily copied.
Test case for recently improved unchecked warning

Prior to https://github.com/scala/scala/pull/2848, the enclosed
test compiled without warning and printed:

    true
    false

Features interacting:
  - implicit class tags to enable type patterns on abstract types
  - type tests on compound types.

I think the unchecked warning is acceptable for now.
SI-8030 force symbols on presentation compiler initialization

This commit forces a number of built-in symbols in presentation
compiler to prevent them from being entered during parsing.

The property “parsing doesn’t enter new symbols” is tested on
a rich source file that contains significant number of variations
of Scala syntax.
Merge pull request #3204 from retronym/topic/patmat-classtag-compound

Test case for recently improved unchecked warning
Merge pull request #3250 from soc/SI-8059

SI-8059 Override immutable.Queue#{+:,:+} for performance
Merge pull request #3262 from densh/si/8030

SI-8030 force symbols on presentation compiler initialization
Merge pull request #3240 from soc/SI-7618

SI-7618 Remove octal number literals