Reduce FormattingOptions to 64 bits

[m-ou-se]

This is part of #99012

This reduces FormattingOptions from 6-7 machine words (384 bits on 64-bit platforms, 224 bits on 32-bit platforms) to just 64 bits (a single register on 64-bit platforms).

This PR includes #136932, which reduces the width and precision options to 16 bits, to make it all fit.

Before:

pub struct FormattingOptions {
    flags: u32, // only 6 bits used
    fill: char,
    align: Option<Alignment>,
    width: Option<usize>,
    precision: Option<usize>,
}

After:

pub struct FormattingOptions {
    /// Bits:
    ///  - 0-20: fill character (21 bits, a full `char`)
    ///  - 21: `+` flag
    ///  - 22: `-` flag
    ///  - 23: `#` flag
    ///  - 24: `0` flag
    ///  - 25: `x?` flag
    ///  - 26: `X?` flag
    ///  - 27: Width flag (if set, the width field below is used)
    ///  - 28: Precision flag (if set, the precision field below is used)
    ///  - 29-30: Alignment (0: Left, 1: Right, 2: Center, 3: Unknown)
    ///  - 31: Always set to 1
    flags: u32,
    /// Width if width flag above is set. Otherwise, always 0.
    width: u16,
    /// Precision if precision flag above is set. Otherwise, always 0.
    precision: u16,
}

[m-ou-se]

@bors try @rust-timer queue

[bors]

⌛ Trying commit c059377 with merge 47853a6...

[bors]

☀️ Try build successful - checks-actions
Build commit: 47853a6 (47853a630ac42e5c5ab5fcd1f07d37eef67f84e9)

[rust-timer]

Finished benchmarking commit (47853a6): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.6%	[0.6%, 0.6%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.4%	[-0.7%, -0.2%]	5
Improvements ✅ (secondary)	-0.5%	[-0.7%, -0.2%]	2
All ❌✅ (primary)	-0.2%	[-0.7%, 0.6%]	6

Max RSS (memory usage)

Results (primary 2.0%, secondary -1.2%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	2.0%	[1.9%, 2.1%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.2%	[-1.2%, -1.2%]	1
All ❌✅ (primary)	2.0%	[1.9%, 2.1%]	2

Cycles

Results (secondary -0.3%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	1.8%	[1.8%, 1.8%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.3%	[-2.3%, -2.3%]	1
All ❌✅ (primary)	-	-	0

Binary size

Results (primary -0.2%, secondary -0.1%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.1%	[0.0%, 0.3%]	6
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.2%	[-0.5%, -0.0%]	70
Improvements ✅ (secondary)	-0.1%	[-0.3%, -0.0%]	56
All ❌✅ (primary)	-0.2%	[-0.5%, 0.3%]	76

Bootstrap: 792.804s -> 787.91s (-0.62%)
Artifact size: 347.85 MiB -> 347.86 MiB (0.00%)

[m-ou-se]

Looks fine. Binary size improvements looking good too: https://perf.rust-lang.org/compare.html?start=54cdc751df770517e70db0588573e32e6a7b9821&end=47853a630ac42e5c5ab5fcd1f07d37eef67f84e9&stat=size%3Alinked_artifact&tab=compile

[m-ou-se]

Marking this as blocked on #136932