In `llvm-cov show`, this option rounds counters (line, branch) to
`[1,0]` at rendering. This will be useful when the number of counts
doesn't interest but **Covered/uncoverd** does.

NFC except for calculating `Total`. I've replaced
`(uint64_t)+(uint64_t)` with `(double)+(double)`.

This is still inexact with large numbers `(1LL << 53)` but will be expected to prevent possible overflow.

Identified with readability-redundant-control-flow.

Currently both True/False counts were folded. It lost the information,
"It is True or False before folding." It prevented recalling branch
counts in merging template instantiations.

In `llvm-cov`, a folded branch is shown as:

- `[True: n, Folded]`
- `[Folded, False n]`

In the case If `n` is zero, a branch is reported as "uncovered". This is
distinguished from "folded" branch. When folded branches are merged,
`Folded` may be dissolved.

In the coverage map, either `Counter` is `Zero`. Currently both were
`Zero`.

Since "partial fold" has been introduced, either case in `switch` is
omitted as `Folded`.

Each `case:` in `switch` is reported as `[True: n, Folded]`, since
`False` count doesn't show meaningful value.

When `switch` doesn't have `default:`, `switch (Cond)` is reported as
`[Folded, False: n]`, since `True` count was just the sum of `case`(s).
`switch` with `default` can be considered as "the statement that doesn't
have any `False`(s)".

I replaced "jump to first uncovered line" with UI buttons and keyboard
shortcut to jump between uncovered parts of code: lines (key L), branchs
(key B), regions (key R).

User can also jump in reverse direction with shift+key.

Personally I use
[cargo-llvm-cov](https://github.com/taiki-e/cargo-llvm-cov) which
creates helpful HTML coverage reports, but they don't support a dynamic
dark themes.

I updated the styling to support both dark and bright color themes based
on the browser preference. The bright theme should look similar to the
current theme.

I also improved some color contrasts (Firefox accessibility tool
reported them) and ensured that line-number links keep their
text-decoration.

Things that both have `.tooltip` and `.red` look kinda odd as the
coloring is now based on tinting with transparency. Given that the
tooltip should always show 0 in such cases (otherwise it wouldn't be
red) the tooltip could be removed there on the HTML generation, but that
seemed out of scope for my style only change.

1. add the missing condition for MC/DC in hasSubViews()
2. add style for selected line
3. remove name="Ln" attribute in the link within MC/DC views
4. remove color for \n

Part 2 of 3. This includes the Visualization and Evaluation components.

Differential Revision: https://reviews.llvm.org/D138847